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 $85.76   10.299%   $94.5924   $94.59   $94.60   $94.60  
  Purchase #2 $202.45   8.539%   $219.7372   $219.74   $219.75   $219.70  
  Purchase #3 $11.91   4.576%   $12.455   $12.46   $12.45   $12.50  
  Purchase #4 $197.29   10.618%   $218.2383   $218.24   $218.25   $218.20  
  Purchase #5 $39.39   10.360%   $43.4708   $43.47   $43.45   $43.50  
  Purchase #6 $246.41   8.528%   $267.4238   $267.42   $267.40   $267.40  
  Purchase #7 $124.62   12.719%   $140.4704   $140.47   $140.45   $140.50  
  7 purchase totals = $907.83       $996.3879   $996.39   $996.35   $996.40