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 $64.37   5.671%   $68.0204   $68.02   $68.00   $68.00  
  Purchase #2 $82.99   13.648%   $94.3165   $94.32   $94.30   $94.30  
  Purchase #3 $147.26   13.561%   $167.2299   $167.23   $167.25   $167.20  
  Purchase #4 $219.86   13.830%   $250.2666   $250.27   $250.25   $250.30  
  Purchase #5 $174.86   5.558%   $184.5787   $184.58   $184.60   $184.60  
  Purchase #6 $7.29   5.687%   $7.7046   $7.70   $7.70   $7.70  
  Purchase #7 $141.44   9.468%   $154.8315   $154.83   $154.85   $154.80  
  7 purchase totals = $838.07       $926.9482   $926.95   $926.95   $926.90