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 $237.95   6.515%   $253.4524   $253.45   $253.45   $253.50  
  Purchase #2 $34.53   13.191%   $39.0849   $39.08   $39.10   $39.10  
  Purchase #3 $108.83   4.196%   $113.3965   $113.40   $113.40   $113.40  
  Purchase #4 $116.45   3.734%   $120.7982   $120.80   $120.80   $120.80  
  Purchase #5 $179.54   3.861%   $186.472   $186.47   $186.45   $186.50  
  Purchase #6 $118.95   13.386%   $134.8726   $134.87   $134.85   $134.90  
  Purchase #7 $159.40   12.431%   $179.215   $179.22   $179.20   $179.20  
  7 purchase totals = $955.65       $1,027.2916   $1,027.29   $1,027.25   $1,027.40