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 $130.46   13.130%   $147.5894   $147.59   $147.60   $147.60  
  Purchase #2 $211.80   11.256%   $235.6402   $235.64   $235.65   $235.60  
  Purchase #3 $223.88   9.285%   $244.6673   $244.67   $244.65   $244.70  
  Purchase #4 $152.61   3.691%   $158.2428   $158.24   $158.25   $158.20  
  Purchase #5 $208.33   10.185%   $229.5484   $229.55   $229.55   $229.50  
  Purchase #6 $51.71   3.669%   $53.6072   $53.61   $53.60   $53.60  
  Purchase #7 $190.32   5.611%   $200.9989   $201.00   $201.00   $201.00  
  7 purchase totals = $1,169.11       $1,270.2942   $1,270.30   $1,270.30   $1,270.20