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 $181.68   6.364%   $193.2421   $193.24   $193.25   $193.20  
  Purchase #2 $210.42   13.444%   $238.7089   $238.71   $238.70   $238.70  
  Purchase #3 $136.65   6.633%   $145.714   $145.71   $145.70   $145.70  
  Purchase #4 $217.76   11.347%   $242.4692   $242.47   $242.45   $242.50  
  Purchase #5 $53.96   5.368%   $56.8566   $56.86   $56.85   $56.90  
  Purchase #6 $40.95   7.363%   $43.9651   $43.97   $43.95   $44.00  
  Purchase #7 $28.42   7.505%   $30.5529   $30.55   $30.55   $30.60  
  7 purchase totals = $869.84       $951.5088   $951.51   $951.45   $951.60