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 $87.97   11.782%   $98.3346   $98.33   $98.35   $98.30  
  Purchase #2 $119.66   13.867%   $136.2533   $136.25   $136.25   $136.30  
  Purchase #3 $67.94   13.130%   $76.8605   $76.86   $76.85   $76.90  
  Purchase #4 $32.89   11.649%   $36.7214   $36.72   $36.70   $36.70  
  Purchase #5 $132.79   4.148%   $138.2981   $138.30   $138.30   $138.30  
  Purchase #6 $102.70   11.592%   $114.605   $114.61   $114.60   $114.60  
  Purchase #7 $70.82   9.367%   $77.4537   $77.45   $77.45   $77.50  
  7 purchase totals = $614.77       $678.5266   $678.52   $678.50   $678.60