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 $112.79   10.376%   $124.4931   $124.49   $124.50   $124.50  
  Purchase #2 $160.78   9.182%   $175.5428   $175.54   $175.55   $175.50  
  Purchase #3 $57.48   3.660%   $59.5838   $59.58   $59.60   $59.60  
  Purchase #4 $218.94   3.779%   $227.2137   $227.21   $227.20   $227.20  
  Purchase #5 $7.39   5.765%   $7.816   $7.82   $7.80   $7.80  
  Purchase #6 $125.35   7.528%   $134.7863   $134.79   $134.80   $134.80  
  Purchase #7 $52.65   9.869%   $57.846   $57.85   $57.85   $57.80  
  7 purchase totals = $735.38       $787.2817   $787.28   $787.30   $787.20