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 $193.41   6.452%   $205.8888   $205.89   $205.90   $205.90  
  Purchase #2 $95.91   10.340%   $105.8271   $105.83   $105.85   $105.80  
  Purchase #3 $110.79   12.255%   $124.3673   $124.37   $124.35   $124.40  
  Purchase #4 $214.88   4.254%   $224.021   $224.02   $224.00   $224.00  
  Purchase #5 $162.41   4.180%   $169.1987   $169.20   $169.20   $169.20  
  Purchase #6 $71.79   12.383%   $80.6798   $80.68   $80.70   $80.70  
  Purchase #7 $243.35   7.547%   $261.7156   $261.72   $261.70   $261.70  
  7 purchase totals = $1,092.54       $1,171.6983   $1,171.71   $1,171.70   $1,171.70