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 $59.97   5.343%   $63.1742   $63.17   $63.15   $63.20  
  Purchase #2 $111.25   8.195%   $120.3669   $120.37   $120.35   $120.40  
  Purchase #3 $200.82   11.739%   $224.3943   $224.39   $224.40   $224.40  
  Purchase #4 $239.41   12.446%   $269.207   $269.21   $269.20   $269.20  
  Purchase #5 $201.98   7.701%   $217.5345   $217.53   $217.55   $217.50  
  Purchase #6 $236.80   3.854%   $245.9263   $245.93   $245.95   $245.90  
  Purchase #7 $220.98   7.800%   $238.2164   $238.22   $238.20   $238.20  
  7 purchase totals = $1,271.21       $1,378.8196   $1,378.82   $1,378.80   $1,378.80