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 $82.85   6.285%   $88.0571   $88.06   $88.05   $88.10  
  Purchase #2 $250.26   4.484%   $261.4817   $261.48   $261.50   $261.50  
  Purchase #3 $198.96   3.323%   $205.5714   $205.57   $205.55   $205.60  
  Purchase #4 $222.67   8.460%   $241.5079   $241.51   $241.50   $241.50  
  Purchase #5 $191.70   10.200%   $211.2534   $211.25   $211.25   $211.30  
  Purchase #6 $235.66   9.262%   $257.4868   $257.49   $257.50   $257.50  
  Purchase #7 $189.61   7.673%   $204.1588   $204.16   $204.15   $204.20  
  7 purchase totals = $1,371.71       $1,469.5171   $1,469.52   $1,469.50   $1,469.70