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 $112.27   9.245%   $122.6494   $122.65   $122.65   $122.60  
  Purchase #2 $60.60   3.645%   $62.8089   $62.81   $62.80   $62.80  
  Purchase #3 $192.51   6.301%   $204.6401   $204.64   $204.65   $204.60  
  Purchase #4 $88.85   9.746%   $97.5093   $97.51   $97.50   $97.50  
  Purchase #5 $7.33   3.168%   $7.5622   $7.56   $7.55   $7.60  
  Purchase #6 $5.83   8.650%   $6.3343   $6.33   $6.35   $6.30  
  Purchase #7 $241.27   3.746%   $250.308   $250.31   $250.30   $250.30  
  7 purchase totals = $708.66       $751.8122   $751.81   $751.80   $751.70