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 $129.36   12.274%   $145.2376   $145.24   $145.25   $145.20  
  Purchase #2 $176.31   8.737%   $191.7142   $191.71   $191.70   $191.70  
  Purchase #3 $208.78   5.594%   $220.4592   $220.46   $220.45   $220.50  
  Purchase #4 $130.93   7.627%   $140.916   $140.92   $140.90   $140.90  
  Purchase #5 $232.29   9.235%   $253.742   $253.74   $253.75   $253.70  
  Purchase #6 $22.27   11.659%   $24.8665   $24.87   $24.85   $24.90  
  Purchase #7 $75.72   4.836%   $79.3818   $79.38   $79.40   $79.40  
  7 purchase totals = $975.66       $1,056.3173   $1,056.32   $1,056.30   $1,056.30