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 $232.80   11.703%   $260.0446   $260.04   $260.05   $260.00  
  Purchase #2 $199.41   3.310%   $206.0105   $206.01   $206.00   $206.00  
  Purchase #3 $12.78   8.865%   $13.9129   $13.91   $13.90   $13.90  
  Purchase #4 $58.35   7.181%   $62.5401   $62.54   $62.55   $62.50  
  Purchase #5 $247.60   12.273%   $277.9879   $277.99   $278.00   $278.00  
  Purchase #6 $150.61   12.642%   $169.6501   $169.65   $169.65   $169.70  
  Purchase #7 $100.26   4.604%   $104.876   $104.88   $104.90   $104.90  
  7 purchase totals = $1,001.81       $1,095.0221   $1,095.02   $1,095.05   $1,095.00