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 $55.59   8.501%   $60.3157   $60.32   $60.30   $60.30  
  Purchase #2 $47.99   3.336%   $49.5909   $49.59   $49.60   $49.60  
  Purchase #3 $228.82   3.829%   $237.5815   $237.58   $237.60   $237.60  
  Purchase #4 $239.31   4.338%   $249.6913   $249.69   $249.70   $249.70  
  Purchase #5 $152.28   8.139%   $164.6741   $164.67   $164.65   $164.70  
  Purchase #6 $14.54   3.210%   $15.0067   $15.01   $15.00   $15.00  
  Purchase #7 $87.48   5.764%   $92.5223   $92.52   $92.50   $92.50  
  7 purchase totals = $826.01       $869.3825   $869.38   $869.35   $869.40