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 $89.72   4.341%   $93.6147   $93.61   $93.60   $93.60  
  Purchase #2 $194.78   5.675%   $205.8338   $205.83   $205.85   $205.80  
  Purchase #3 $62.38   8.749%   $67.8376   $67.84   $67.85   $67.80  
  Purchase #4 $174.96   7.547%   $188.1642   $188.16   $188.15   $188.20  
  Purchase #5 $110.72   8.407%   $120.0282   $120.03   $120.05   $120.00  
  Purchase #6 $200.72   5.531%   $211.8218   $211.82   $211.80   $211.80  
  Purchase #7 $117.74   13.788%   $133.974   $133.97   $133.95   $134.00  
  7 purchase totals = $951.02       $1,021.2743   $1,021.26   $1,021.25   $1,021.20