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 $225.47   12.213%   $253.0067   $253.01   $253.00   $253.00  
  Purchase #2 $212.33   10.682%   $235.0111   $235.01   $235.00   $235.00  
  Purchase #3 $139.77   11.705%   $156.1301   $156.13   $156.15   $156.10  
  Purchase #4 $174.58   10.761%   $193.3666   $193.37   $193.35   $193.40  
  Purchase #5 $155.48   6.450%   $165.5085   $165.51   $165.50   $165.50  
  Purchase #6 $67.64   3.552%   $70.0426   $70.04   $70.05   $70.00  
  Purchase #7 $207.42   12.298%   $232.9285   $232.93   $232.95   $232.90  
  7 purchase totals = $1,182.69       $1,305.9941   $1,306.00   $1,306.00   $1,305.90