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 $208.94   12.638%   $235.3458   $235.35   $235.35   $235.30  
  Purchase #2 $82.43   12.526%   $92.7552   $92.76   $92.75   $92.80  
  Purchase #3 $85.96   4.600%   $89.9142   $89.91   $89.90   $89.90  
  Purchase #4 $237.52   6.716%   $253.4718   $253.47   $253.45   $253.50  
  Purchase #5 $169.44   10.605%   $187.4091   $187.41   $187.40   $187.40  
  Purchase #6 $241.35   4.278%   $251.675   $251.68   $251.70   $251.70  
  Purchase #7 $46.79   8.257%   $50.6535   $50.65   $50.65   $50.70  
  7 purchase totals = $1,072.43       $1,161.2246   $1,161.23   $1,161.20   $1,161.30