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 $201.85   5.244%   $212.435   $212.44   $212.45   $212.40  
  Purchase #2 $18.30   10.684%   $20.2552   $20.26   $20.25   $20.30  
  Purchase #3 $30.73   3.462%   $31.7939   $31.79   $31.80   $31.80  
  Purchase #4 $192.68   6.243%   $204.709   $204.71   $204.70   $204.70  
  Purchase #5 $34.50   5.361%   $36.3495   $36.35   $36.35   $36.30  
  Purchase #6 $203.89   10.805%   $225.9203   $225.92   $225.90   $225.90  
  Purchase #7 $248.83   10.426%   $274.773   $274.77   $274.75   $274.80  
  7 purchase totals = $930.78       $1,006.2359   $1,006.24   $1,006.20   $1,006.20