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 $242.82   13.673%   $276.0208   $276.02   $276.00   $276.00  
  Purchase #2 $90.52   8.481%   $98.197   $98.20   $98.20   $98.20  
  Purchase #3 $214.92   11.623%   $239.9002   $239.90   $239.90   $239.90  
  Purchase #4 $230.92   10.553%   $255.289   $255.29   $255.30   $255.30  
  Purchase #5 $138.47   9.676%   $151.8684   $151.87   $151.85   $151.90  
  Purchase #6 $94.25   8.662%   $102.4139   $102.41   $102.40   $102.40  
  Purchase #7 $6.87   10.402%   $7.5846   $7.58   $7.60   $7.60  
  7 purchase totals = $1,018.77       $1,131.2739   $1,131.27   $1,131.25   $1,131.30