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 $63.82   3.374%   $65.9733   $65.97   $65.95   $66.00  
  Purchase #2 $47.36   5.159%   $49.8033   $49.80   $49.80   $49.80  
  Purchase #3 $96.32   5.380%   $101.502   $101.50   $101.50   $101.50  
  Purchase #4 $36.44   3.740%   $37.8029   $37.80   $37.80   $37.80  
  Purchase #5 $212.37   9.638%   $232.8382   $232.84   $232.85   $232.80  
  Purchase #6 $89.67   7.245%   $96.1666   $96.17   $96.15   $96.20  
  Purchase #7 $109.48   4.772%   $114.7044   $114.70   $114.70   $114.70  
  7 purchase totals = $655.46       $698.7907   $698.78   $698.75   $698.80