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 $61.73   8.759%   $67.1369   $67.14   $67.15   $67.10  
  Purchase #2 $219.56   6.320%   $233.4362   $233.44   $233.45   $233.40  
  Purchase #3 $222.44   9.752%   $244.1323   $244.13   $244.15   $244.10  
  Purchase #4 $200.65   9.774%   $220.2615   $220.26   $220.25   $220.30  
  Purchase #5 $90.58   7.484%   $97.359   $97.36   $97.35   $97.40  
  Purchase #6 $174.95   10.769%   $193.7904   $193.79   $193.80   $193.80  
  Purchase #7 $244.80   12.580%   $275.5958   $275.60   $275.60   $275.60  
  7 purchase totals = $1,214.71       $1,331.7121   $1,331.72   $1,331.75   $1,331.70