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 $57.34   5.817%   $60.6755   $60.68   $60.70   $60.70  
  Purchase #2 $130.94   9.306%   $143.1253   $143.13   $143.15   $143.10  
  Purchase #3 $203.41   6.860%   $217.3639   $217.36   $217.35   $217.40  
  Purchase #4 $97.88   9.853%   $107.5241   $107.52   $107.50   $107.50  
  Purchase #5 $242.46   7.759%   $261.2725   $261.27   $261.25   $261.30  
  Purchase #6 $59.50   3.425%   $61.5379   $61.54   $61.55   $61.50  
  Purchase #7 $186.30   7.551%   $200.3675   $200.37   $200.35   $200.40  
  7 purchase totals = $977.83       $1,051.8667   $1,051.87   $1,051.85   $1,051.90