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 $10.95   3.429%   $11.3255   $11.33   $11.35   $11.30  
  Purchase #2 $179.92   7.266%   $192.993   $192.99   $193.00   $193.00  
  Purchase #3 $15.48   9.746%   $16.9887   $16.99   $17.00   $17.00  
  Purchase #4 $83.50   3.299%   $86.2547   $86.25   $86.25   $86.30  
  Purchase #5 $142.46   9.378%   $155.8199   $155.82   $155.80   $155.80  
  Purchase #6 $187.26   12.421%   $210.5196   $210.52   $210.50   $210.50  
  Purchase #7 $219.41   5.725%   $231.9712   $231.97   $231.95   $232.00  
  7 purchase totals = $838.98       $905.8726   $905.87   $905.85   $905.90