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 $34.27   10.246%   $37.7813   $37.78   $37.80   $37.80  
  Purchase #2 $239.83   5.734%   $253.5819   $253.58   $253.60   $253.60  
  Purchase #3 $6.47   6.121%   $6.866   $6.87   $6.85   $6.90  
  Purchase #4 $146.39   12.710%   $164.9962   $165.00   $165.00   $165.00  
  Purchase #5 $168.66   6.246%   $179.1945   $179.19   $179.20   $179.20  
  Purchase #6 $173.90   3.865%   $180.6212   $180.62   $180.60   $180.60  
  Purchase #7 $225.90   4.443%   $235.9367   $235.94   $235.95   $235.90  
  7 purchase totals = $995.42       $1,058.9778   $1,058.98   $1,059.00   $1,059.00