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 $97.73   6.140%   $103.7306   $103.73   $103.75   $103.70  
  Purchase #2 $139.78   12.646%   $157.4566   $157.46   $157.45   $157.50  
  Purchase #3 $183.28   10.534%   $202.5867   $202.59   $202.60   $202.60  
  Purchase #4 $72.46   11.716%   $80.9494   $80.95   $80.95   $80.90  
  Purchase #5 $186.74   6.713%   $199.2759   $199.28   $199.30   $199.30  
  Purchase #6 $151.51   12.634%   $170.6518   $170.65   $170.65   $170.70  
  Purchase #7 $245.99   6.704%   $262.4812   $262.48   $262.50   $262.50  
  7 purchase totals = $1,077.49       $1,177.1322   $1,177.14   $1,177.20   $1,177.20