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 $188.76   13.727%   $214.6711   $214.67   $214.65   $214.70  
  Purchase #2 $201.98   3.296%   $208.6373   $208.64   $208.65   $208.60  
  Purchase #3 $235.50   4.807%   $246.8205   $246.82   $246.80   $246.80  
  Purchase #4 $25.68   12.367%   $28.8558   $28.86   $28.85   $28.90  
  Purchase #5 $162.58   8.731%   $176.7749   $176.77   $176.75   $176.80  
  Purchase #6 $225.76   13.514%   $256.2692   $256.27   $256.25   $256.30  
  Purchase #7 $209.74   11.726%   $234.3341   $234.33   $234.35   $234.30  
  7 purchase totals = $1,250.00       $1,366.3629   $1,366.36   $1,366.30   $1,366.40