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 $241.95   5.639%   $255.5936   $255.59   $255.60   $255.60  
  Purchase #2 $67.69   6.424%   $72.0384   $72.04   $72.05   $72.00  
  Purchase #3 $150.61   3.456%   $155.8151   $155.82   $155.80   $155.80  
  Purchase #4 $159.95   3.410%   $165.4043   $165.40   $165.40   $165.40  
  Purchase #5 $246.78   8.724%   $268.3091   $268.31   $268.30   $268.30  
  Purchase #6 $189.53   9.642%   $207.8045   $207.80   $207.80   $207.80  
  Purchase #7 $211.49   11.109%   $234.9844   $234.98   $235.00   $235.00  
  7 purchase totals = $1,268.00       $1,359.9494   $1,359.94   $1,359.95   $1,359.90