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 $134.55   8.477%   $145.9558   $145.96   $145.95   $146.00  
  Purchase #2 $180.28   3.755%   $187.0495   $187.05   $187.05   $187.00  
  Purchase #3 $202.54   9.389%   $221.5565   $221.56   $221.55   $221.60  
  Purchase #4 $127.57   4.586%   $133.4204   $133.42   $133.40   $133.40  
  Purchase #5 $195.29   9.685%   $214.2038   $214.20   $214.20   $214.20  
  Purchase #6 $199.79   13.269%   $226.3001   $226.30   $226.30   $226.30  
  Purchase #7 $241.76   9.845%   $265.5613   $265.56   $265.55   $265.60  
  7 purchase totals = $1,281.78       $1,394.0474   $1,394.05   $1,394.00   $1,394.10