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 $108.27   10.594%   $119.7401   $119.74   $119.75   $119.70  
  Purchase #2 $47.54   4.350%   $49.608   $49.61   $49.60   $49.60  
  Purchase #3 $142.43   3.351%   $147.2028   $147.20   $147.20   $147.20  
  Purchase #4 $228.66   8.245%   $247.513   $247.51   $247.50   $247.50  
  Purchase #5 $44.68   13.678%   $50.7913   $50.79   $50.80   $50.80  
  Purchase #6 $130.38   6.728%   $139.152   $139.15   $139.15   $139.20  
  Purchase #7 $6.77   13.715%   $7.6985   $7.70   $7.70   $7.70  
  7 purchase totals = $708.73       $761.7057   $761.70   $761.70   $761.70