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 $96.76   5.855%   $102.4253   $102.43   $102.45   $102.40  
  Purchase #2 $154.47   13.433%   $175.22   $175.22   $175.20   $175.20  
  Purchase #3 $23.52   8.468%   $25.5117   $25.51   $25.50   $25.50  
  Purchase #4 $144.82   13.110%   $163.8059   $163.81   $163.80   $163.80  
  Purchase #5 $54.45   11.583%   $60.7569   $60.76   $60.75   $60.80  
  Purchase #6 $158.56   12.693%   $178.686   $178.69   $178.70   $178.70  
  Purchase #7 $48.76   8.331%   $52.8222   $52.82   $52.80   $52.80  
  7 purchase totals = $681.34       $759.2280   $759.24   $759.20   $759.20