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 $61.37   13.254%   $69.504   $69.50   $69.50   $69.50  
  Purchase #2 $132.69   13.569%   $150.6947   $150.69   $150.70   $150.70  
  Purchase #3 $84.39   13.500%   $95.7827   $95.78   $95.80   $95.80  
  Purchase #4 $95.45   4.340%   $99.5925   $99.59   $99.60   $99.60  
  Purchase #5 $175.97   8.674%   $191.2336   $191.23   $191.25   $191.20  
  Purchase #6 $174.53   8.261%   $188.9479   $188.95   $188.95   $188.90  
  Purchase #7 $30.90   3.558%   $31.9994   $32.00   $32.00   $32.00  
  7 purchase totals = $755.30       $827.7548   $827.74   $827.80   $827.70