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 $68.62   11.733%   $76.6712   $76.67   $76.65   $76.70  
  Purchase #2 $240.96   4.151%   $250.9622   $250.96   $250.95   $251.00  
  Purchase #3 $198.86   13.258%   $225.2249   $225.22   $225.20   $225.20  
  Purchase #4 $199.46   8.486%   $216.3862   $216.39   $216.40   $216.40  
  Purchase #5 $19.50   4.584%   $20.3939   $20.39   $20.40   $20.40  
  Purchase #6 $73.30   3.598%   $75.9373   $75.94   $75.95   $75.90  
  Purchase #7 $129.97   10.771%   $143.9691   $143.97   $143.95   $144.00  
  7 purchase totals = $930.67       $1,009.5448   $1,009.54   $1,009.50   $1,009.60