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 $60.27   3.442%   $62.3445   $62.34   $62.35   $62.30  
  Purchase #2 $39.71   7.362%   $42.6335   $42.63   $42.65   $42.60  
  Purchase #3 $236.73   4.722%   $247.9084   $247.91   $247.90   $247.90  
  Purchase #4 $123.33   9.241%   $134.7269   $134.73   $134.75   $134.70  
  Purchase #5 $90.51   5.397%   $95.3948   $95.39   $95.40   $95.40  
  Purchase #6 $34.52   6.233%   $36.6716   $36.67   $36.65   $36.70  
  Purchase #7 $50.86   13.278%   $57.6132   $57.61   $57.60   $57.60  
  7 purchase totals = $635.93       $677.2929   $677.28   $677.30   $677.20