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 $159.76   13.833%   $181.8596   $181.86   $181.85   $181.90  
  Purchase #2 $151.38   5.176%   $159.2154   $159.22   $159.20   $159.20  
  Purchase #3 $98.33   6.586%   $104.806   $104.81   $104.80   $104.80  
  Purchase #4 $158.62   6.752%   $169.33   $169.33   $169.35   $169.30  
  Purchase #5 $207.89   12.865%   $234.635   $234.64   $234.65   $234.60  
  Purchase #6 $60.53   7.459%   $65.0449   $65.04   $65.05   $65.00  
  Purchase #7 $17.72   3.315%   $18.3074   $18.31   $18.30   $18.30  
  7 purchase totals = $854.23       $933.1983   $933.21   $933.20   $933.10