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 $248.77   5.166%   $261.6215   $261.62   $261.60   $261.60  
  Purchase #2 $157.55   5.524%   $166.2531   $166.25   $166.25   $166.30  
  Purchase #3 $72.97   5.861%   $77.2468   $77.25   $77.25   $77.20  
  Purchase #4 $184.52   4.872%   $193.5098   $193.51   $193.50   $193.50  
  Purchase #5 $212.38   3.371%   $219.5393   $219.54   $219.55   $219.50  
  Purchase #6 $216.47   9.475%   $236.9805   $236.98   $237.00   $237.00  
  Purchase #7 $35.65   11.222%   $39.6506   $39.65   $39.65   $39.70  
  7 purchase totals = $1,128.31       $1,194.8016   $1,194.80   $1,194.80   $1,194.80