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 $60.59   8.768%   $65.9025   $65.90   $65.90   $65.90  
  Purchase #2 $125.87   8.465%   $136.5249   $136.52   $136.50   $136.50  
  Purchase #3 $44.33   7.113%   $47.4832   $47.48   $47.50   $47.50  
  Purchase #4 $233.35   10.525%   $257.9101   $257.91   $257.90   $257.90  
  Purchase #5 $137.68   13.393%   $156.1195   $156.12   $156.10   $156.10  
  Purchase #6 $167.26   12.482%   $188.1374   $188.14   $188.15   $188.10  
  Purchase #7 $66.36   6.408%   $70.6123   $70.61   $70.60   $70.60  
  7 purchase totals = $835.44       $922.6899   $922.68   $922.65   $922.60