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 $48.69   6.642%   $51.924   $51.92   $51.90   $51.90  
  Purchase #2 $52.33   7.647%   $56.3317   $56.33   $56.35   $56.30  
  Purchase #3 $180.52   8.167%   $195.2631   $195.26   $195.25   $195.30  
  Purchase #4 $96.73   7.759%   $104.2353   $104.24   $104.25   $104.20  
  Purchase #5 $44.25   7.156%   $47.4165   $47.42   $47.40   $47.40  
  Purchase #6 $229.98   6.584%   $245.1219   $245.12   $245.10   $245.10  
  Purchase #7 $54.92   8.646%   $59.6684   $59.67   $59.65   $59.70  
  7 purchase totals = $707.42       $759.9609   $759.96   $759.90   $759.90