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 $104.42   13.801%   $118.831   $118.83   $118.85   $118.80  
  Purchase #2 $167.48   4.661%   $175.2862   $175.29   $175.30   $175.30  
  Purchase #3 $98.29   4.764%   $102.9725   $102.97   $102.95   $103.00  
  Purchase #4 $70.26   4.154%   $73.1786   $73.18   $73.20   $73.20  
  Purchase #5 $15.61   4.433%   $16.302   $16.30   $16.30   $16.30  
  Purchase #6 $182.74   6.553%   $194.715   $194.72   $194.70   $194.70  
  Purchase #7 $115.76   13.284%   $131.1376   $131.14   $131.15   $131.10  
  7 purchase totals = $754.56       $812.4229   $812.43   $812.45   $812.40