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 $59.61   9.722%   $65.4053   $65.41   $65.40   $65.40  
  Purchase #2 $151.36   13.443%   $171.7073   $171.71   $171.70   $171.70  
  Purchase #3 $81.83   6.339%   $87.0172   $87.02   $87.00   $87.00  
  Purchase #4 $198.49   13.197%   $224.6847   $224.68   $224.70   $224.70  
  Purchase #5 $196.96   6.471%   $209.7053   $209.71   $209.70   $209.70  
  Purchase #6 $203.86   7.556%   $219.2637   $219.26   $219.25   $219.30  
  Purchase #7 $89.67   8.166%   $96.9925   $96.99   $97.00   $97.00  
  7 purchase totals = $981.78       $1,074.7760   $1,074.78   $1,074.75   $1,074.80