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 $66.97   11.474%   $74.6541   $74.65   $74.65   $74.70  
  Purchase #2 $111.42   9.497%   $122.0016   $122.00   $122.00   $122.00  
  Purchase #3 $235.61   6.207%   $250.2343   $250.23   $250.25   $250.20  
  Purchase #4 $17.91   6.261%   $19.0313   $19.03   $19.05   $19.00  
  Purchase #5 $78.36   11.156%   $87.1018   $87.10   $87.10   $87.10  
  Purchase #6 $149.71   12.179%   $167.9432   $167.94   $167.95   $167.90  
  Purchase #7 $22.82   7.421%   $24.5135   $24.51   $24.50   $24.50  
  7 purchase totals = $682.80       $745.4798   $745.46   $745.50   $745.40