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 $31.95   8.542%   $34.6792   $34.68   $34.70   $34.70  
  Purchase #2 $220.76   4.386%   $230.4425   $230.44   $230.45   $230.40  
  Purchase #3 $181.38   4.361%   $189.29   $189.29   $189.30   $189.30  
  Purchase #4 $205.45   8.274%   $222.4489   $222.45   $222.45   $222.40  
  Purchase #5 $11.75   5.725%   $12.4227   $12.42   $12.40   $12.40  
  Purchase #6 $198.48   5.813%   $210.0176   $210.02   $210.00   $210.00  
  Purchase #7 $13.26   8.735%   $14.4183   $14.42   $14.40   $14.40  
  7 purchase totals = $863.03       $913.7192   $913.72   $913.70   $913.60