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 $42.90   8.652%   $46.6117   $46.61   $46.60   $46.60  
  Purchase #2 $101.53   8.654%   $110.3164   $110.32   $110.30   $110.30  
  Purchase #3 $178.44   8.743%   $194.041   $194.04   $194.05   $194.00  
  Purchase #4 $51.74   13.405%   $58.6757   $58.68   $58.70   $58.70  
  Purchase #5 $209.74   7.324%   $225.1014   $225.10   $225.10   $225.10  
  Purchase #6 $242.56   8.190%   $262.4257   $262.43   $262.45   $262.40  
  Purchase #7 $113.40   4.754%   $118.791   $118.79   $118.80   $118.80  
  7 purchase totals = $940.31       $1,015.9629   $1,015.97   $1,016.00   $1,015.90