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 $240.84   8.660%   $261.6967   $261.70   $261.70   $261.70  
  Purchase #2 $145.42   7.733%   $156.6653   $156.67   $156.65   $156.70  
  Purchase #3 $19.45   10.760%   $21.5428   $21.54   $21.55   $21.50  
  Purchase #4 $56.65   6.130%   $60.1226   $60.12   $60.10   $60.10  
  Purchase #5 $205.99   6.296%   $218.9591   $218.96   $218.95   $219.00  
  Purchase #6 $114.71   10.323%   $126.5515   $126.55   $126.55   $126.60  
  Purchase #7 $89.80   5.319%   $94.5765   $94.58   $94.60   $94.60  
  7 purchase totals = $872.86       $940.1145   $940.12   $940.10   $940.20