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 $112.49   5.519%   $118.6983   $118.70   $118.70   $118.70  
  Purchase #2 $176.82   10.861%   $196.0244   $196.02   $196.00   $196.00  
  Purchase #3 $161.42   4.715%   $169.031   $169.03   $169.05   $169.00  
  Purchase #4 $176.95   7.149%   $189.6002   $189.60   $189.60   $189.60  
  Purchase #5 $250.58   7.754%   $270.01   $270.01   $270.00   $270.00  
  Purchase #6 $212.94   6.386%   $226.5383   $226.54   $226.55   $226.50  
  Purchase #7 $195.95   11.108%   $217.7161   $217.72   $217.70   $217.70  
  7 purchase totals = $1,287.15       $1,387.6183   $1,387.62   $1,387.60   $1,387.50