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 $213.53   8.573%   $231.8359   $231.84   $231.85   $231.80  
  Purchase #2 $192.76   3.573%   $199.6473   $199.65   $199.65   $199.60  
  Purchase #3 $40.50   11.343%   $45.0939   $45.09   $45.10   $45.10  
  Purchase #4 $26.44   9.459%   $28.941   $28.94   $28.95   $28.90  
  Purchase #5 $241.94   3.445%   $250.2748   $250.27   $250.25   $250.30  
  Purchase #6 $236.41   11.234%   $262.9683   $262.97   $262.95   $263.00  
  Purchase #7 $169.80   4.258%   $177.0301   $177.03   $177.05   $177.00  
  7 purchase totals = $1,121.38       $1,195.7913   $1,195.79   $1,195.80   $1,195.70