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 $23.73   13.340%   $26.8956   $26.90   $26.90   $26.90  
  Purchase #2 $196.97   6.429%   $209.6332   $209.63   $209.65   $209.60  
  Purchase #3 $167.39   11.136%   $186.0306   $186.03   $186.05   $186.00  
  Purchase #4 $235.62   13.489%   $267.4028   $267.40   $267.40   $267.40  
  Purchase #5 $138.50   11.712%   $154.7211   $154.72   $154.70   $154.70  
  Purchase #6 $136.91   10.187%   $150.857   $150.86   $150.85   $150.90  
  Purchase #7 $56.91   7.634%   $61.2545   $61.25   $61.25   $61.30  
  7 purchase totals = $956.03       $1,056.7948   $1,056.79   $1,056.80   $1,056.80