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 $208.31   12.364%   $234.0654   $234.07   $234.05   $234.10  
  Purchase #2 $13.33   8.618%   $14.4788   $14.48   $14.50   $14.50  
  Purchase #3 $77.35   13.745%   $87.9818   $87.98   $88.00   $88.00  
  Purchase #4 $58.48   3.822%   $60.7151   $60.72   $60.70   $60.70  
  Purchase #5 $76.53   11.496%   $85.3279   $85.33   $85.35   $85.30  
  Purchase #6 $35.85   7.752%   $38.6291   $38.63   $38.65   $38.60  
  Purchase #7 $36.80   11.857%   $41.1634   $41.16   $41.15   $41.20  
  7 purchase totals = $506.65       $562.3615   $562.37   $562.40   $562.40