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 $230.36   13.578%   $261.6383   $261.64   $261.65   $261.60  
  Purchase #2 $204.57   3.137%   $210.9874   $210.99   $211.00   $211.00  
  Purchase #3 $99.52   5.865%   $105.3568   $105.36   $105.35   $105.40  
  Purchase #4 $72.67   7.218%   $77.9153   $77.92   $77.90   $77.90  
  Purchase #5 $124.61   4.618%   $130.3645   $130.36   $130.35   $130.40  
  Purchase #6 $197.79   4.646%   $206.9793   $206.98   $207.00   $207.00  
  Purchase #7 $26.38   8.466%   $28.6133   $28.61   $28.60   $28.60  
  7 purchase totals = $955.90       $1,021.8549   $1,021.86   $1,021.85   $1,021.90