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 $227.58   6.137%   $241.5466   $241.55   $241.55   $241.50  
  Purchase #2 $66.91   3.427%   $69.203   $69.20   $69.20   $69.20  
  Purchase #3 $212.98   11.622%   $237.7325   $237.73   $237.75   $237.70  
  Purchase #4 $22.91   5.663%   $24.2074   $24.21   $24.20   $24.20  
  Purchase #5 $237.69   8.346%   $257.5276   $257.53   $257.55   $257.50  
  Purchase #6 $25.77   4.600%   $26.9554   $26.96   $26.95   $27.00  
  Purchase #7 $177.82   8.625%   $193.157   $193.16   $193.15   $193.20  
  7 purchase totals = $971.66       $1,050.3295   $1,050.34   $1,050.35   $1,050.30