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 $85.72   9.718%   $94.0503   $94.05   $94.05   $94.10  
  Purchase #2 $197.91   4.346%   $206.5112   $206.51   $206.50   $206.50  
  Purchase #3 $18.34   12.141%   $20.5667   $20.57   $20.55   $20.60  
  Purchase #4 $185.46   11.717%   $207.1903   $207.19   $207.20   $207.20  
  Purchase #5 $195.26   4.235%   $203.5293   $203.53   $203.55   $203.50  
  Purchase #6 $43.37   10.807%   $48.057   $48.06   $48.05   $48.10  
  Purchase #7 $208.26   5.806%   $220.3516   $220.35   $220.35   $220.40  
  7 purchase totals = $934.32       $1,000.2564   $1,000.26   $1,000.25   $1,000.40