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 $65.41   8.536%   $70.9934   $70.99   $71.00   $71.00  
  Purchase #2 $107.93   4.667%   $112.9671   $112.97   $112.95   $113.00  
  Purchase #3 $238.36   5.571%   $251.639   $251.64   $251.65   $251.60  
  Purchase #4 $50.65   5.575%   $53.4737   $53.47   $53.45   $53.50  
  Purchase #5 $166.98   9.580%   $182.9767   $182.98   $183.00   $183.00  
  Purchase #6 $174.65   10.663%   $193.2729   $193.27   $193.25   $193.30  
  Purchase #7 $217.39   4.137%   $226.3834   $226.38   $226.40   $226.40  
  7 purchase totals = $1,021.37       $1,091.7062   $1,091.70   $1,091.70   $1,091.80