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 $183.77   8.261%   $198.9512   $198.95   $198.95   $199.00  
  Purchase #2 $73.89   3.658%   $76.5929   $76.59   $76.60   $76.60  
  Purchase #3 $191.82   7.331%   $205.8823   $205.88   $205.90   $205.90  
  Purchase #4 $173.36   10.303%   $191.2213   $191.22   $191.20   $191.20  
  Purchase #5 $170.32   4.744%   $178.4   $178.40   $178.40   $178.40  
  Purchase #6 $17.84   8.666%   $19.386   $19.39   $19.40   $19.40  
  Purchase #7 $126.32   3.193%   $130.3534   $130.35   $130.35   $130.40  
  7 purchase totals = $937.32       $1,000.7871   $1,000.78   $1,000.80   $1,000.90