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 $84.79   9.532%   $92.8722   $92.87   $92.85   $92.90  
  Purchase #2 $87.28   10.518%   $96.4601   $96.46   $96.45   $96.50  
  Purchase #3 $247.91   13.348%   $281.001   $281.00   $281.00   $281.00  
  Purchase #4 $87.26   11.718%   $97.4851   $97.49   $97.50   $97.50  
  Purchase #5 $207.63   8.356%   $224.9796   $224.98   $225.00   $225.00  
  Purchase #6 $53.72   7.421%   $57.7066   $57.71   $57.70   $57.70  
  Purchase #7 $183.89   5.767%   $194.4949   $194.49   $194.50   $194.50  
  7 purchase totals = $952.48       $1,044.9995   $1,045.00   $1,045.00   $1,045.10