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 $42.57   10.768%   $47.1539   $47.15   $47.15   $47.20  
  Purchase #2 $219.48   7.378%   $235.6732   $235.67   $235.65   $235.70  
  Purchase #3 $112.50   6.584%   $119.907   $119.91   $119.90   $119.90  
  Purchase #4 $56.91   6.710%   $60.7287   $60.73   $60.75   $60.70  
  Purchase #5 $233.59   7.662%   $251.4877   $251.49   $251.50   $251.50  
  Purchase #6 $107.59   9.467%   $117.7755   $117.78   $117.80   $117.80  
  Purchase #7 $92.35   13.414%   $104.7378   $104.74   $104.75   $104.70  
  7 purchase totals = $864.99       $937.4638   $937.47   $937.50   $937.50