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 $58.31   11.634%   $65.0938   $65.09   $65.10   $65.10  
  Purchase #2 $229.42   13.186%   $259.6713   $259.67   $259.65   $259.70  
  Purchase #3 $146.61   10.177%   $161.5305   $161.53   $161.55   $161.50  
  Purchase #4 $183.90   4.339%   $191.8794   $191.88   $191.90   $191.90  
  Purchase #5 $193.73   9.600%   $212.3281   $212.33   $212.35   $212.30  
  Purchase #6 $143.87   11.710%   $160.7172   $160.72   $160.70   $160.70  
  Purchase #7 $41.48   8.397%   $44.9631   $44.96   $44.95   $45.00  
  7 purchase totals = $997.32       $1,096.1834   $1,096.18   $1,096.20   $1,096.20