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 $216.49   8.111%   $234.0495   $234.05   $234.05   $234.00  
  Purchase #2 $22.61   13.196%   $25.5936   $25.59   $25.60   $25.60  
  Purchase #3 $60.94   6.107%   $64.6616   $64.66   $64.65   $64.70  
  Purchase #4 $138.36   3.389%   $143.049   $143.05   $143.05   $143.00  
  Purchase #5 $25.77   9.813%   $28.2988   $28.30   $28.30   $28.30  
  Purchase #6 $156.99   8.222%   $169.8977   $169.90   $169.90   $169.90  
  Purchase #7 $49.26   13.344%   $55.8333   $55.83   $55.85   $55.80  
  7 purchase totals = $670.42       $721.3835   $721.38   $721.40   $721.30