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 $85.68   10.411%   $94.6001   $94.60   $94.60   $94.60  
  Purchase #2 $84.55   5.139%   $88.895   $88.90   $88.90   $88.90  
  Purchase #3 $60.63   8.408%   $65.7278   $65.73   $65.75   $65.70  
  Purchase #4 $88.31   6.492%   $94.0431   $94.04   $94.05   $94.00  
  Purchase #5 $30.83   12.484%   $34.6788   $34.68   $34.70   $34.70  
  Purchase #6 $138.60   13.517%   $157.3346   $157.33   $157.35   $157.30  
  Purchase #7 $128.75   10.696%   $142.5211   $142.52   $142.50   $142.50  
  7 purchase totals = $617.35       $677.8005   $677.80   $677.85   $677.70