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 $61.53   6.277%   $65.3922   $65.39   $65.40   $65.40  
  Purchase #2 $23.81   13.863%   $27.1108   $27.11   $27.10   $27.10  
  Purchase #3 $87.50   6.497%   $93.1849   $93.18   $93.20   $93.20  
  Purchase #4 $193.35   11.301%   $215.2005   $215.20   $215.20   $215.20  
  Purchase #5 $189.31   13.448%   $214.7684   $214.77   $214.75   $214.80  
  Purchase #6 $104.47   6.711%   $111.481   $111.48   $111.50   $111.50  
  Purchase #7 $219.56   3.291%   $226.7857   $226.79   $226.80   $226.80  
  7 purchase totals = $879.53       $953.9235   $953.92   $953.95   $954.00