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 $241.61   7.307%   $259.2644   $259.26   $259.25   $259.30  
  Purchase #2 $123.38   8.359%   $133.6933   $133.69   $133.70   $133.70  
  Purchase #3 $239.28   10.358%   $264.0646   $264.06   $264.05   $264.10  
  Purchase #4 $146.52   11.229%   $162.9727   $162.97   $162.95   $163.00  
  Purchase #5 $11.31   12.545%   $12.7288   $12.73   $12.75   $12.70  
  Purchase #6 $166.92   6.759%   $178.2021   $178.20   $178.20   $178.20  
  Purchase #7 $244.88   4.621%   $256.1959   $256.20   $256.20   $256.20  
  7 purchase totals = $1,173.90       $1,267.1218   $1,267.11   $1,267.10   $1,267.20