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 $234.70   13.749%   $266.9689   $266.97   $266.95   $267.00  
  Purchase #2 $177.65   13.872%   $202.2936   $202.29   $202.30   $202.30  
  Purchase #3 $148.70   11.728%   $166.1395   $166.14   $166.15   $166.10  
  Purchase #4 $151.46   7.152%   $162.2924   $162.29   $162.30   $162.30  
  Purchase #5 $121.49   5.528%   $128.206   $128.21   $128.20   $128.20  
  Purchase #6 $192.77   10.327%   $212.6774   $212.68   $212.70   $212.70  
  Purchase #7 $100.64   7.696%   $108.3853   $108.39   $108.40   $108.40  
  7 purchase totals = $1,127.41       $1,246.9631   $1,246.97   $1,247.00   $1,247.00