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 $58.72   6.372%   $62.4616   $62.46   $62.45   $62.50  
  Purchase #2 $59.75   9.463%   $65.4041   $65.40   $65.40   $65.40  
  Purchase #3 $224.65   9.118%   $245.1336   $245.13   $245.15   $245.10  
  Purchase #4 $58.63   5.107%   $61.6242   $61.62   $61.60   $61.60  
  Purchase #5 $157.56   6.595%   $167.9511   $167.95   $167.95   $168.00  
  Purchase #6 $208.96   11.167%   $232.2946   $232.29   $232.30   $232.30  
  Purchase #7 $80.99   13.587%   $91.9941   $91.99   $92.00   $92.00  
  7 purchase totals = $849.26       $926.8633   $926.84   $926.85   $926.90