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 $82.45   11.216%   $91.6976   $91.70   $91.70   $91.70  
  Purchase #2 $16.30   12.862%   $18.3965   $18.40   $18.40   $18.40  
  Purchase #3 $95.33   4.173%   $99.3081   $99.31   $99.30   $99.30  
  Purchase #4 $174.70   7.255%   $187.3745   $187.37   $187.35   $187.40  
  Purchase #5 $196.36   5.807%   $207.7626   $207.76   $207.75   $207.80  
  Purchase #6 $169.36   6.634%   $180.5953   $180.60   $180.60   $180.60  
  Purchase #7 $152.85   7.845%   $164.8411   $164.84   $164.85   $164.80  
  7 purchase totals = $887.35       $949.9757   $949.98   $949.95   $950.00