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 $202.50   11.292%   $225.3663   $225.37   $225.35   $225.40  
  Purchase #2 $37.62   3.777%   $39.0409   $39.04   $39.05   $39.00  
  Purchase #3 $96.92   5.464%   $102.2157   $102.22   $102.20   $102.20  
  Purchase #4 $8.35   3.620%   $8.6523   $8.65   $8.65   $8.70  
  Purchase #5 $208.69   12.447%   $234.6656   $234.67   $234.65   $234.70  
  Purchase #6 $55.67   5.111%   $58.5153   $58.52   $58.50   $58.50  
  Purchase #7 $68.69   11.318%   $76.4643   $76.46   $76.45   $76.50  
  7 purchase totals = $678.44       $744.9204   $744.93   $744.85   $745.00