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 $195.70   8.487%   $212.3091   $212.31   $212.30   $212.30  
  Purchase #2 $113.98   12.157%   $127.8365   $127.84   $127.85   $127.80  
  Purchase #3 $56.53   7.196%   $60.5979   $60.60   $60.60   $60.60  
  Purchase #4 $32.67   11.390%   $36.3911   $36.39   $36.40   $36.40  
  Purchase #5 $228.49   7.413%   $245.428   $245.43   $245.45   $245.40  
  Purchase #6 $205.80   7.435%   $221.1012   $221.10   $221.10   $221.10  
  Purchase #7 $98.77   13.514%   $112.1178   $112.12   $112.10   $112.10  
  7 purchase totals = $931.94       $1,015.7816   $1,015.79   $1,015.80   $1,015.70