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 $106.82   8.768%   $116.186   $116.19   $116.20   $116.20  
  Purchase #2 $64.72   6.535%   $68.9495   $68.95   $68.95   $68.90  
  Purchase #3 $219.54   7.349%   $235.674   $235.67   $235.65   $235.70  
  Purchase #4 $83.95   12.511%   $94.453   $94.45   $94.45   $94.50  
  Purchase #5 $190.43   4.437%   $198.8794   $198.88   $198.90   $198.90  
  Purchase #6 $236.96   13.366%   $268.6321   $268.63   $268.65   $268.60  
  Purchase #7 $112.90   13.696%   $128.3628   $128.36   $128.35   $128.40  
  7 purchase totals = $1,015.32       $1,111.1368   $1,111.13   $1,111.15   $1,111.20