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 $61.52   13.541%   $69.8504   $69.85   $69.85   $69.90  
  Purchase #2 $215.25   4.167%   $224.2195   $224.22   $224.20   $224.20  
  Purchase #3 $92.26   6.249%   $98.0253   $98.03   $98.05   $98.00  
  Purchase #4 $26.42   3.826%   $27.4308   $27.43   $27.45   $27.40  
  Purchase #5 $71.44   13.468%   $81.0615   $81.06   $81.05   $81.10  
  Purchase #6 $243.46   11.839%   $272.2832   $272.28   $272.30   $272.30  
  Purchase #7 $80.52   13.408%   $91.3161   $91.32   $91.30   $91.30  
  7 purchase totals = $790.87       $864.1868   $864.19   $864.20   $864.20