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 $67.66   9.651%   $74.1899   $74.19   $74.20   $74.20  
  Purchase #2 $62.45   7.150%   $66.9152   $66.92   $66.90   $66.90  
  Purchase #3 $167.92   5.442%   $177.0582   $177.06   $177.05   $177.10  
  Purchase #4 $194.65   7.312%   $208.8828   $208.88   $208.90   $208.90  
  Purchase #5 $124.41   13.252%   $140.8968   $140.90   $140.90   $140.90  
  Purchase #6 $113.59   10.310%   $125.3011   $125.30   $125.30   $125.30  
  Purchase #7 $198.93   8.147%   $215.1368   $215.14   $215.15   $215.10  
  7 purchase totals = $929.61       $1,008.3808   $1,008.39   $1,008.40   $1,008.40