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 $55.36   8.847%   $60.2577   $60.26   $60.25   $60.30  
  Purchase #2 $227.44   12.269%   $255.3446   $255.34   $255.35   $255.30  
  Purchase #3 $183.69   6.744%   $196.0781   $196.08   $196.10   $196.10  
  Purchase #4 $33.36   9.474%   $36.5205   $36.52   $36.50   $36.50  
  Purchase #5 $42.88   13.623%   $48.7215   $48.72   $48.70   $48.70  
  Purchase #6 $142.71   9.382%   $156.0991   $156.10   $156.10   $156.10  
  Purchase #7 $86.35   10.209%   $95.1655   $95.17   $95.15   $95.20  
  7 purchase totals = $771.79       $848.1870   $848.19   $848.15   $848.20