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 $84.71   8.109%   $91.5791   $91.58   $91.60   $91.60  
  Purchase #2 $206.41   5.425%   $217.6077   $217.61   $217.60   $217.60  
  Purchase #3 $169.40   8.116%   $183.1485   $183.15   $183.15   $183.10  
  Purchase #4 $113.31   7.584%   $121.9034   $121.90   $121.90   $121.90  
  Purchase #5 $22.78   12.728%   $25.6794   $25.68   $25.70   $25.70  
  Purchase #6 $91.43   5.294%   $96.2703   $96.27   $96.25   $96.30  
  Purchase #7 $206.40   6.477%   $219.7685   $219.77   $219.75   $219.80  
  7 purchase totals = $894.44       $955.9569   $955.96   $955.95   $956.00