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 $59.39   9.761%   $65.1871   $65.19   $65.20   $65.20  
  Purchase #2 $9.79   11.197%   $10.8862   $10.89   $10.90   $10.90  
  Purchase #3 $104.39   12.326%   $117.2571   $117.26   $117.25   $117.30  
  Purchase #4 $12.29   12.527%   $13.8296   $13.83   $13.85   $13.80  
  Purchase #5 $232.65   11.809%   $260.1236   $260.12   $260.10   $260.10  
  Purchase #6 $174.34   9.477%   $190.8622   $190.86   $190.85   $190.90  
  Purchase #7 $192.39   13.423%   $218.2145   $218.21   $218.20   $218.20  
  7 purchase totals = $785.24       $876.3603   $876.36   $876.35   $876.40