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 $245.54   3.149%   $253.2721   $253.27   $253.25   $253.30  
  Purchase #2 $197.82   7.504%   $212.6644   $212.66   $212.65   $212.70  
  Purchase #3 $150.45   13.359%   $170.5486   $170.55   $170.55   $170.50  
  Purchase #4 $250.26   9.695%   $274.5227   $274.52   $274.50   $274.50  
  Purchase #5 $131.99   4.175%   $137.5006   $137.50   $137.50   $137.50  
  Purchase #6 $229.32   3.874%   $238.2039   $238.20   $238.20   $238.20  
  Purchase #7 $237.30   3.449%   $245.4845   $245.48   $245.50   $245.50  
  7 purchase totals = $1,442.68       $1,532.1968   $1,532.18   $1,532.15   $1,532.20