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 $89.63   11.858%   $100.2583   $100.26   $100.25   $100.30  
  Purchase #2 $220.57   6.540%   $234.9953   $235.00   $235.00   $235.00  
  Purchase #3 $218.52   12.319%   $245.4395   $245.44   $245.45   $245.40  
  Purchase #4 $66.58   9.536%   $72.9291   $72.93   $72.95   $72.90  
  Purchase #5 $214.32   3.474%   $221.7655   $221.77   $221.75   $221.80  
  Purchase #6 $173.47   7.567%   $186.5965   $186.60   $186.60   $186.60  
  Purchase #7 $98.86   7.631%   $106.404   $106.40   $106.40   $106.40  
  7 purchase totals = $1,081.95       $1,168.3882   $1,168.40   $1,168.40   $1,168.40