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 $213.74   13.189%   $241.9302   $241.93   $241.95   $241.90  
  Purchase #2 $203.78   11.553%   $227.3227   $227.32   $227.30   $227.30  
  Purchase #3 $206.84   9.716%   $226.9366   $226.94   $226.95   $226.90  
  Purchase #4 $170.27   4.736%   $178.334   $178.33   $178.35   $178.30  
  Purchase #5 $83.80   11.506%   $93.442   $93.44   $93.45   $93.40  
  Purchase #6 $127.70   4.334%   $133.2345   $133.23   $133.25   $133.20  
  Purchase #7 $20.28   6.599%   $21.6183   $21.62   $21.60   $21.60  
  7 purchase totals = $1,026.41       $1,122.8183   $1,122.81   $1,122.85   $1,122.60