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 $247.86   11.635%   $276.6985   $276.70   $276.70   $276.70  
  Purchase #2 $197.34   11.264%   $219.5684   $219.57   $219.55   $219.60  
  Purchase #3 $232.55   3.854%   $241.5125   $241.51   $241.50   $241.50  
  Purchase #4 $103.54   7.210%   $111.0052   $111.01   $111.00   $111.00  
  Purchase #5 $132.71   6.274%   $141.0362   $141.04   $141.05   $141.00  
  Purchase #6 $119.99   6.642%   $127.9597   $127.96   $127.95   $128.00  
  Purchase #7 $83.29   4.182%   $86.7732   $86.77   $86.75   $86.80  
  7 purchase totals = $1,117.28       $1,204.5537   $1,204.56   $1,204.50   $1,204.60