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 $226.67   3.335%   $234.2294   $234.23   $234.25   $234.20  
  Purchase #2 $221.73   9.419%   $242.6147   $242.61   $242.60   $242.60  
  Purchase #3 $67.54   7.848%   $72.8405   $72.84   $72.85   $72.80  
  Purchase #4 $141.53   11.400%   $157.6644   $157.66   $157.65   $157.70  
  Purchase #5 $61.64   6.380%   $65.5726   $65.57   $65.55   $65.60  
  Purchase #6 $61.62   6.334%   $65.523   $65.52   $65.50   $65.50  
  Purchase #7 $180.50   9.577%   $197.7865   $197.79   $197.80   $197.80  
  7 purchase totals = $961.23       $1,036.2311   $1,036.22   $1,036.20   $1,036.20