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 $64.65   12.171%   $72.5186   $72.52   $72.50   $72.50  
  Purchase #2 $110.63   8.126%   $119.6198   $119.62   $119.60   $119.60  
  Purchase #3 $194.36   4.826%   $203.7398   $203.74   $203.75   $203.70  
  Purchase #4 $81.84   10.144%   $90.1418   $90.14   $90.15   $90.10  
  Purchase #5 $222.96   11.524%   $248.6539   $248.65   $248.65   $248.70  
  Purchase #6 $20.64   9.869%   $22.677   $22.68   $22.70   $22.70  
  Purchase #7 $64.45   5.441%   $67.9567   $67.96   $67.95   $68.00  
  7 purchase totals = $759.53       $825.3076   $825.31   $825.30   $825.30