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 $114.84   6.681%   $122.5125   $122.51   $122.50   $122.50  
  Purchase #2 $96.54   13.219%   $109.3016   $109.30   $109.30   $109.30  
  Purchase #3 $214.32   12.172%   $240.407   $240.41   $240.40   $240.40  
  Purchase #4 $65.48   4.625%   $68.5085   $68.51   $68.50   $68.50  
  Purchase #5 $90.63   9.823%   $99.5326   $99.53   $99.55   $99.50  
  Purchase #6 $133.73   11.814%   $149.5289   $149.53   $149.55   $149.50  
  Purchase #7 $235.35   3.785%   $244.258   $244.26   $244.25   $244.30  
  7 purchase totals = $950.89       $1,034.0491   $1,034.05   $1,034.05   $1,034.00