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 $91.64   6.611%   $97.6983   $97.70   $97.70   $97.70  
  Purchase #2 $109.34   6.332%   $116.2634   $116.26   $116.25   $116.30  
  Purchase #3 $195.37   3.348%   $201.911   $201.91   $201.90   $201.90  
  Purchase #4 $181.54   6.703%   $193.7086   $193.71   $193.70   $193.70  
  Purchase #5 $112.96   4.197%   $117.7009   $117.70   $117.70   $117.70  
  Purchase #6 $25.71   10.642%   $28.4461   $28.45   $28.45   $28.40  
  Purchase #7 $15.78   3.405%   $16.3173   $16.32   $16.30   $16.30  
  7 purchase totals = $732.34       $772.0456   $772.05   $772.00   $772.00