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 $214.60   4.173%   $223.5553   $223.56   $223.55   $223.60  
  Purchase #2 $199.46   10.237%   $219.8787   $219.88   $219.90   $219.90  
  Purchase #3 $23.81   10.560%   $26.3243   $26.32   $26.30   $26.30  
  Purchase #4 $78.42   11.504%   $87.4414   $87.44   $87.45   $87.40  
  Purchase #5 $202.35   11.332%   $225.2803   $225.28   $225.30   $225.30  
  Purchase #6 $79.94   9.799%   $87.7733   $87.77   $87.75   $87.80  
  Purchase #7 $158.84   8.105%   $171.714   $171.71   $171.70   $171.70  
  7 purchase totals = $957.42       $1,041.9673   $1,041.96   $1,041.95   $1,042.00