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 $221.52   6.243%   $235.3495   $235.35   $235.35   $235.30  
  Purchase #2 $194.71   6.123%   $206.6321   $206.63   $206.65   $206.60  
  Purchase #3 $228.26   11.576%   $254.6834   $254.68   $254.70   $254.70  
  Purchase #4 $209.61   3.276%   $216.4768   $216.48   $216.50   $216.50  
  Purchase #5 $59.48   7.490%   $63.9351   $63.94   $63.95   $63.90  
  Purchase #6 $16.55   6.368%   $17.6039   $17.60   $17.60   $17.60  
  Purchase #7 $185.83   3.119%   $191.626   $191.63   $191.65   $191.60  
  7 purchase totals = $1,115.96       $1,186.3068   $1,186.31   $1,186.40   $1,186.20