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 $171.98   6.599%   $183.329   $183.33   $183.35   $183.30  
  Purchase #2 $49.36   8.129%   $53.3725   $53.37   $53.35   $53.40  
  Purchase #3 $100.33   8.580%   $108.9383   $108.94   $108.95   $108.90  
  Purchase #4 $239.98   9.271%   $262.2285   $262.23   $262.25   $262.20  
  Purchase #5 $183.77   11.821%   $205.4935   $205.49   $205.50   $205.50  
  Purchase #6 $204.56   9.461%   $223.9134   $223.91   $223.90   $223.90  
  Purchase #7 $89.81   8.169%   $97.1466   $97.15   $97.15   $97.10  
  7 purchase totals = $1,039.79       $1,134.4218   $1,134.42   $1,134.45   $1,134.30