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 $57.55   11.716%   $64.2926   $64.29   $64.30   $64.30  
  Purchase #2 $56.80   8.152%   $61.4303   $61.43   $61.45   $61.40  
  Purchase #3 $146.50   10.744%   $162.24   $162.24   $162.25   $162.20  
  Purchase #4 $111.90   13.520%   $127.0289   $127.03   $127.05   $127.00  
  Purchase #5 $34.27   7.517%   $36.8461   $36.85   $36.85   $36.80  
  Purchase #6 $98.79   3.638%   $102.384   $102.38   $102.40   $102.40  
  Purchase #7 $194.83   3.516%   $201.6802   $201.68   $201.70   $201.70  
  7 purchase totals = $700.64       $755.9021   $755.90   $756.00   $755.80