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 $63.64   5.843%   $67.3585   $67.36   $67.35   $67.40  
  Purchase #2 $154.59   10.714%   $171.1528   $171.15   $171.15   $171.20  
  Purchase #3 $195.98   4.416%   $204.6345   $204.63   $204.65   $204.60  
  Purchase #4 $173.34   10.592%   $191.7002   $191.70   $191.70   $191.70  
  Purchase #5 $123.92   5.634%   $130.9017   $130.90   $130.90   $130.90  
  Purchase #6 $184.76   10.595%   $204.3353   $204.34   $204.35   $204.30  
  Purchase #7 $243.51   7.598%   $262.0119   $262.01   $262.00   $262.00  
  7 purchase totals = $1,139.74       $1,232.0949   $1,232.09   $1,232.10   $1,232.10