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 $125.43   6.246%   $133.2644   $133.26   $133.25   $133.30  
  Purchase #2 $190.52   6.163%   $202.2617   $202.26   $202.25   $202.30  
  Purchase #3 $228.37   11.756%   $255.2172   $255.22   $255.20   $255.20  
  Purchase #4 $197.53   7.714%   $212.7675   $212.77   $212.75   $212.80  
  Purchase #5 $63.69   5.602%   $67.2579   $67.26   $67.25   $67.30  
  Purchase #6 $184.79   11.299%   $205.6694   $205.67   $205.65   $205.70  
  Purchase #7 $25.99   3.589%   $26.9228   $26.92   $26.90   $26.90  
  7 purchase totals = $1,016.32       $1,103.3609   $1,103.36   $1,103.25   $1,103.50