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 $60.60   11.125%   $67.3418   $67.34   $67.35   $67.30  
  Purchase #2 $233.86   5.394%   $246.4744   $246.47   $246.45   $246.50  
  Purchase #3 $79.55   10.186%   $87.653   $87.65   $87.65   $87.70  
  Purchase #4 $62.91   5.628%   $66.4506   $66.45   $66.45   $66.50  
  Purchase #5 $11.71   11.660%   $13.0754   $13.08   $13.10   $13.10  
  Purchase #6 $113.64   8.514%   $123.3153   $123.32   $123.30   $123.30  
  Purchase #7 $85.88   8.869%   $93.4967   $93.50   $93.50   $93.50  
  7 purchase totals = $648.15       $697.8072   $697.81   $697.80   $697.90