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 $82.88   11.536%   $92.441   $92.44   $92.45   $92.40  
  Purchase #2 $118.63   4.570%   $124.0514   $124.05   $124.05   $124.10  
  Purchase #3 $109.38   13.861%   $124.5412   $124.54   $124.55   $124.50  
  Purchase #4 $93.64   6.833%   $100.0384   $100.04   $100.05   $100.00  
  Purchase #5 $237.70   11.379%   $264.7479   $264.75   $264.75   $264.70  
  Purchase #6 $188.46   5.556%   $198.9308   $198.93   $198.95   $198.90  
  Purchase #7 $118.41   6.420%   $126.0119   $126.01   $126.00   $126.00  
  7 purchase totals = $949.10       $1,030.7626   $1,030.76   $1,030.80   $1,030.60