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 $236.86   9.447%   $259.2362   $259.24   $259.25   $259.20  
  Purchase #2 $115.25   13.324%   $130.6059   $130.61   $130.60   $130.60  
  Purchase #3 $197.59   7.607%   $212.6207   $212.62   $212.60   $212.60  
  Purchase #4 $210.70   8.344%   $228.2808   $228.28   $228.30   $228.30  
  Purchase #5 $235.32   9.154%   $256.8612   $256.86   $256.85   $256.90  
  Purchase #6 $192.90   7.264%   $206.9123   $206.91   $206.90   $206.90  
  Purchase #7 $184.87   9.504%   $202.44   $202.44   $202.45   $202.40  
  7 purchase totals = $1,373.49       $1,496.9571   $1,496.96   $1,496.95   $1,496.90