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 $169.74   12.316%   $190.6452   $190.65   $190.65   $190.60  
  Purchase #2 $154.77   13.378%   $175.4751   $175.48   $175.50   $175.50  
  Purchase #3 $193.80   5.376%   $204.2187   $204.22   $204.20   $204.20  
  Purchase #4 $93.51   4.740%   $97.9424   $97.94   $97.95   $97.90  
  Purchase #5 $196.48   9.279%   $214.7114   $214.71   $214.70   $214.70  
  Purchase #6 $245.46   9.402%   $268.5381   $268.54   $268.55   $268.50  
  Purchase #7 $97.35   7.146%   $104.3066   $104.31   $104.30   $104.30  
  7 purchase totals = $1,151.11       $1,255.8375   $1,255.85   $1,255.85   $1,255.70