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 $126.83   6.238%   $134.7417   $134.74   $134.75   $134.70  
  Purchase #2 $25.52   3.564%   $26.4295   $26.43   $26.45   $26.40  
  Purchase #3 $169.69   4.777%   $177.7961   $177.80   $177.80   $177.80  
  Purchase #4 $182.63   6.632%   $194.742   $194.74   $194.75   $194.70  
  Purchase #5 $110.98   7.619%   $119.4356   $119.44   $119.45   $119.40  
  Purchase #6 $133.30   5.367%   $140.4542   $140.45   $140.45   $140.50  
  Purchase #7 $60.74   13.457%   $68.9138   $68.91   $68.90   $68.90  
  7 purchase totals = $809.69       $862.5129   $862.51   $862.55   $862.40