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 $54.56   4.675%   $57.1107   $57.11   $57.10   $57.10  
  Purchase #2 $77.59   11.421%   $86.4516   $86.45   $86.45   $86.50  
  Purchase #3 $152.26   6.117%   $161.5737   $161.57   $161.55   $161.60  
  Purchase #4 $110.97   8.136%   $119.9985   $120.00   $120.00   $120.00  
  Purchase #5 $85.92   12.691%   $96.8241   $96.82   $96.80   $96.80  
  Purchase #6 $230.93   13.625%   $262.3942   $262.39   $262.40   $262.40  
  Purchase #7 $143.36   13.283%   $162.4025   $162.40   $162.40   $162.40  
  7 purchase totals = $855.59       $946.7553   $946.74   $946.70   $946.80