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 $64.82   3.295%   $66.9558   $66.96   $66.95   $67.00  
  Purchase #2 $22.89   5.560%   $24.1627   $24.16   $24.15   $24.20  
  Purchase #3 $98.75   4.638%   $103.33   $103.33   $103.35   $103.30  
  Purchase #4 $198.95   13.333%   $225.476   $225.48   $225.50   $225.50  
  Purchase #5 $149.99   13.654%   $170.4696   $170.47   $170.45   $170.50  
  Purchase #6 $187.47   8.126%   $202.7038   $202.70   $202.70   $202.70  
  Purchase #7 $63.34   5.247%   $66.6634   $66.66   $66.65   $66.70  
  7 purchase totals = $786.21       $859.7613   $859.76   $859.75   $859.90