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 $231.28   9.788%   $253.9177   $253.92   $253.90   $253.90  
  Purchase #2 $62.95   7.272%   $67.5277   $67.53   $67.55   $67.50  
  Purchase #3 $32.52   13.426%   $36.8861   $36.89   $36.90   $36.90  
  Purchase #4 $8.41   5.229%   $8.8498   $8.85   $8.85   $8.80  
  Purchase #5 $194.87   5.717%   $206.0107   $206.01   $206.00   $206.00  
  Purchase #6 $118.46   13.299%   $134.214   $134.21   $134.20   $134.20  
  Purchase #7 $48.72   9.107%   $53.1569   $53.16   $53.15   $53.20  
  7 purchase totals = $697.21       $760.5629   $760.57   $760.55   $760.50