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 $246.84   8.581%   $268.0213   $268.02   $268.00   $268.00  
  Purchase #2 $186.92   4.130%   $194.6398   $194.64   $194.65   $194.60  
  Purchase #3 $150.93   10.166%   $166.2735   $166.27   $166.25   $166.30  
  Purchase #4 $248.41   8.494%   $269.5099   $269.51   $269.50   $269.50  
  Purchase #5 $206.81   3.351%   $213.7402   $213.74   $213.75   $213.70  
  Purchase #6 $50.72   12.715%   $57.169   $57.17   $57.15   $57.20  
  Purchase #7 $163.37   8.828%   $177.7923   $177.79   $177.80   $177.80  
  7 purchase totals = $1,254.00       $1,347.1460   $1,347.14   $1,347.10   $1,347.10