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 $92.58   3.836%   $96.1314   $96.13   $96.15   $96.10  
  Purchase #2 $114.93   3.573%   $119.0364   $119.04   $119.05   $119.00  
  Purchase #3 $64.35   3.514%   $66.6113   $66.61   $66.60   $66.60  
  Purchase #4 $118.81   8.527%   $128.9409   $128.94   $128.95   $128.90  
  Purchase #5 $23.70   12.442%   $26.6488   $26.65   $26.65   $26.60  
  Purchase #6 $245.26   6.363%   $260.8659   $260.87   $260.85   $260.90  
  Purchase #7 $168.99   12.159%   $189.5375   $189.54   $189.55   $189.50  
  7 purchase totals = $828.62       $887.7722   $887.78   $887.80   $887.60