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 $31.77   12.108%   $35.6167   $35.62   $35.60   $35.60  
  Purchase #2 $227.88   6.235%   $242.0883   $242.09   $242.10   $242.10  
  Purchase #3 $225.72   7.601%   $242.877   $242.88   $242.90   $242.90  
  Purchase #4 $161.72   8.414%   $175.3271   $175.33   $175.35   $175.30  
  Purchase #5 $155.96   12.385%   $175.2756   $175.28   $175.30   $175.30  
  Purchase #6 $210.87   8.774%   $229.3717   $229.37   $229.35   $229.40  
  Purchase #7 $241.66   10.412%   $266.8216   $266.82   $266.80   $266.80  
  7 purchase totals = $1,255.58       $1,367.3780   $1,367.39   $1,367.40   $1,367.40