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 $187.57   10.186%   $206.6759   $206.68   $206.70   $206.70  
  Purchase #2 $232.38   13.269%   $263.2145   $263.21   $263.20   $263.20  
  Purchase #3 $55.60   12.614%   $62.6134   $62.61   $62.60   $62.60  
  Purchase #4 $175.97   13.359%   $199.4778   $199.48   $199.50   $199.50  
  Purchase #5 $162.43   11.834%   $181.652   $181.65   $181.65   $181.70  
  Purchase #6 $220.70   13.568%   $250.6446   $250.64   $250.65   $250.60  
  Purchase #7 $164.94   9.477%   $180.5714   $180.57   $180.55   $180.60  
  7 purchase totals = $1,199.59       $1,344.8496   $1,344.84   $1,344.85   $1,344.90