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 $57.44   9.473%   $62.8813   $62.88   $62.90   $62.90  
  Purchase #2 $35.86   6.723%   $38.2709   $38.27   $38.25   $38.30  
  Purchase #3 $93.28   5.268%   $98.194   $98.19   $98.20   $98.20  
  Purchase #4 $200.99   11.446%   $223.9953   $224.00   $224.00   $224.00  
  Purchase #5 $148.95   11.125%   $165.5207   $165.52   $165.50   $165.50  
  Purchase #6 $138.95   9.155%   $151.6709   $151.67   $151.65   $151.70  
  Purchase #7 $225.37   8.537%   $244.6098   $244.61   $244.60   $244.60  
  7 purchase totals = $900.84       $985.1429   $985.14   $985.10   $985.20