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 $93.34   5.728%   $98.6865   $98.69   $98.70   $98.70  
  Purchase #2 $26.49   12.334%   $29.7573   $29.76   $29.75   $29.80  
  Purchase #3 $18.87   6.737%   $20.1413   $20.14   $20.15   $20.10  
  Purchase #4 $205.77   11.272%   $228.9644   $228.96   $228.95   $229.00  
  Purchase #5 $96.30   4.175%   $100.3205   $100.32   $100.30   $100.30  
  Purchase #6 $187.83   5.637%   $198.418   $198.42   $198.40   $198.40  
  Purchase #7 $61.65   11.669%   $68.8439   $68.84   $68.85   $68.80  
  7 purchase totals = $690.25       $745.1319   $745.13   $745.10   $745.10