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 $30.34   12.284%   $34.067   $34.07   $34.05   $34.10  
  Purchase #2 $203.81   6.610%   $217.2818   $217.28   $217.30   $217.30  
  Purchase #3 $19.95   10.291%   $22.0031   $22.00   $22.00   $22.00  
  Purchase #4 $126.83   9.156%   $138.4426   $138.44   $138.45   $138.40  
  Purchase #5 $55.29   11.415%   $61.6014   $61.60   $61.60   $61.60  
  Purchase #6 $164.49   8.196%   $177.9716   $177.97   $177.95   $178.00  
  Purchase #7 $219.99   11.292%   $244.8313   $244.83   $244.85   $244.80  
  7 purchase totals = $820.70       $896.1988   $896.19   $896.20   $896.20