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 $67.29   9.592%   $73.7445   $73.74   $73.75   $73.70  
  Purchase #2 $224.47   3.822%   $233.0492   $233.05   $233.05   $233.00  
  Purchase #3 $61.83   6.748%   $66.0023   $66.00   $66.00   $66.00  
  Purchase #4 $72.36   3.840%   $75.1386   $75.14   $75.15   $75.10  
  Purchase #5 $203.36   4.584%   $212.682   $212.68   $212.70   $212.70  
  Purchase #6 $13.89   13.228%   $15.7274   $15.73   $15.75   $15.70  
  Purchase #7 $130.99   13.832%   $149.1085   $149.11   $149.10   $149.10  
  7 purchase totals = $774.19       $825.4525   $825.45   $825.50   $825.30