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 $24.64   6.348%   $26.2041   $26.20   $26.20   $26.20  
  Purchase #2 $184.92   6.814%   $197.5204   $197.52   $197.50   $197.50  
  Purchase #3 $88.39   8.270%   $95.6999   $95.70   $95.70   $95.70  
  Purchase #4 $137.52   12.119%   $154.186   $154.19   $154.20   $154.20  
  Purchase #5 $242.62   5.649%   $256.3256   $256.33   $256.35   $256.30  
  Purchase #6 $104.39   11.547%   $116.4439   $116.44   $116.45   $116.40  
  Purchase #7 $239.35   13.363%   $271.3343   $271.33   $271.35   $271.30  
  7 purchase totals = $1,021.83       $1,117.7142   $1,117.71   $1,117.75   $1,117.60