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 $216.61   13.636%   $246.1469   $246.15   $246.15   $246.10  
  Purchase #2 $33.28   3.620%   $34.4847   $34.48   $34.50   $34.50  
  Purchase #3 $54.83   10.711%   $60.7028   $60.70   $60.70   $60.70  
  Purchase #4 $56.53   3.245%   $58.3644   $58.36   $58.35   $58.40  
  Purchase #5 $113.72   11.284%   $126.5522   $126.55   $126.55   $126.60  
  Purchase #6 $95.84   4.701%   $100.3454   $100.35   $100.35   $100.30  
  Purchase #7 $104.87   13.742%   $119.2812   $119.28   $119.30   $119.30  
  7 purchase totals = $675.68       $745.8776   $745.87   $745.90   $745.90