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 $118.70   13.400%   $134.6058   $134.61   $134.60   $134.60  
  Purchase #2 $193.98   9.133%   $211.6962   $211.70   $211.70   $211.70  
  Purchase #3 $45.34   6.460%   $48.269   $48.27   $48.25   $48.30  
  Purchase #4 $246.73   13.543%   $280.1446   $280.14   $280.15   $280.10  
  Purchase #5 $26.43   12.427%   $29.7145   $29.71   $29.70   $29.70  
  Purchase #6 $117.51   13.605%   $133.4972   $133.50   $133.50   $133.50  
  Purchase #7 $43.95   4.844%   $46.0789   $46.08   $46.10   $46.10  
  7 purchase totals = $792.64       $884.0062   $884.01   $884.00   $884.00