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 $52.64   8.204%   $56.9586   $56.96   $56.95   $57.00  
  Purchase #2 $235.91   4.793%   $247.2172   $247.22   $247.20   $247.20  
  Purchase #3 $137.87   7.126%   $147.6946   $147.69   $147.70   $147.70  
  Purchase #4 $217.47   9.208%   $237.4946   $237.49   $237.50   $237.50  
  Purchase #5 $182.44   13.366%   $206.8249   $206.82   $206.80   $206.80  
  Purchase #6 $234.25   13.181%   $265.1265   $265.13   $265.15   $265.10  
  Purchase #7 $137.88   9.420%   $150.8683   $150.87   $150.85   $150.90  
  7 purchase totals = $1,198.46       $1,312.1847   $1,312.18   $1,312.15   $1,312.20