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 $239.51   11.103%   $266.1028   $266.10   $266.10   $266.10  
  Purchase #2 $172.75   7.113%   $185.0377   $185.04   $185.05   $185.00  
  Purchase #3 $22.78   8.210%   $24.6502   $24.65   $24.65   $24.70  
  Purchase #4 $198.98   10.874%   $220.6171   $220.62   $220.60   $220.60  
  Purchase #5 $147.95   7.557%   $159.1306   $159.13   $159.15   $159.10  
  Purchase #6 $210.86   9.476%   $230.8411   $230.84   $230.85   $230.80  
  Purchase #7 $74.73   10.610%   $82.6589   $82.66   $82.65   $82.70  
  7 purchase totals = $1,067.56       $1,169.0384   $1,169.04   $1,169.05   $1,169.00