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 $85.67   13.648%   $97.3622   $97.36   $97.35   $97.40  
  Purchase #2 $21.73   7.164%   $23.2867   $23.29   $23.30   $23.30  
  Purchase #3 $131.28   8.763%   $142.7841   $142.78   $142.80   $142.80  
  Purchase #4 $41.54   4.273%   $43.315   $43.32   $43.30   $43.30  
  Purchase #5 $138.93   6.113%   $147.4228   $147.42   $147.40   $147.40  
  Purchase #6 $232.82   12.388%   $261.6617   $261.66   $261.65   $261.70  
  Purchase #7 $204.59   12.736%   $230.6466   $230.65   $230.65   $230.60  
  7 purchase totals = $856.56       $946.4791   $946.48   $946.45   $946.50