Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $158.34   6.202%   $168.1602   $168.16   $168.15   $168.20  
  Purchase #2 $128.35   13.132%   $145.2049   $145.20   $145.20   $145.20  
  Purchase #3 $246.34   11.179%   $273.8783   $273.88   $273.90   $273.90  
  Purchase #4 $233.78   12.696%   $263.4607   $263.46   $263.45   $263.50  
  Purchase #5 $188.70   12.668%   $212.6045   $212.60   $212.60   $212.60  
  Purchase #6 $238.91   5.161%   $251.2401   $251.24   $251.25   $251.20  
  Purchase #7 $170.55   9.102%   $186.0735   $186.07   $186.05   $186.10  
  7 purchase totals = $1,364.97       $1,500.6222   $1,500.61   $1,500.60   $1,500.70