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 $82.88   10.848%   $91.8708   $91.87   $91.85   $91.90  
  Purchase #2 $32.87   7.598%   $35.3675   $35.37   $35.35   $35.40  
  Purchase #3 $236.32   3.508%   $244.6101   $244.61   $244.60   $244.60  
  Purchase #4 $197.71   4.677%   $206.9569   $206.96   $206.95   $207.00  
  Purchase #5 $56.29   10.118%   $61.9854   $61.99   $62.00   $62.00  
  Purchase #6 $186.60   5.419%   $196.7119   $196.71   $196.70   $196.70  
  Purchase #7 $92.71   3.850%   $96.2793   $96.28   $96.30   $96.30  
  7 purchase totals = $885.38       $933.7819   $933.79   $933.75   $933.90