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 $192.71   4.540%   $201.459   $201.46   $201.45   $201.50  
  Purchase #2 $43.77   12.716%   $49.3358   $49.34   $49.35   $49.30  
  Purchase #3 $139.88   12.388%   $157.2083   $157.21   $157.20   $157.20  
  Purchase #4 $234.52   12.341%   $263.4621   $263.46   $263.45   $263.50  
  Purchase #5 $179.29   3.264%   $185.142   $185.14   $185.15   $185.10  
  Purchase #6 $229.30   5.340%   $241.5446   $241.54   $241.55   $241.50  
  Purchase #7 $166.31   12.364%   $186.8726   $186.87   $186.85   $186.90  
  7 purchase totals = $1,185.78       $1,285.0244   $1,285.02   $1,285.00   $1,285.00