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 $78.36   13.136%   $88.6534   $88.65   $88.65   $88.70  
  Purchase #2 $157.80   10.545%   $174.44   $174.44   $174.45   $174.40  
  Purchase #3 $194.43   10.426%   $214.7013   $214.70   $214.70   $214.70  
  Purchase #4 $187.59   11.421%   $209.0147   $209.01   $209.00   $209.00  
  Purchase #5 $124.68   4.769%   $130.626   $130.63   $130.65   $130.60  
  Purchase #6 $54.33   7.573%   $58.4444   $58.44   $58.45   $58.40  
  Purchase #7 $240.87   11.241%   $267.9462   $267.95   $267.95   $267.90  
  7 purchase totals = $1,038.06       $1,143.8260   $1,143.82   $1,143.85   $1,143.70