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 $228.78   8.518%   $248.2675   $248.27   $248.25   $248.30  
  Purchase #2 $219.86   4.674%   $230.1363   $230.14   $230.15   $230.10  
  Purchase #3 $154.33   8.207%   $166.9959   $167.00   $167.00   $167.00  
  Purchase #4 $151.38   13.731%   $172.166   $172.17   $172.15   $172.20  
  Purchase #5 $202.93   10.345%   $223.9231   $223.92   $223.90   $223.90  
  Purchase #6 $166.79   12.612%   $187.8256   $187.83   $187.85   $187.80  
  Purchase #7 $194.69   12.481%   $218.9893   $218.99   $219.00   $219.00  
  7 purchase totals = $1,318.76       $1,448.3037   $1,448.32   $1,448.30   $1,448.30