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 $71.90   4.701%   $75.28   $75.28   $75.30   $75.30  
  Purchase #2 $93.87   5.416%   $98.954   $98.95   $98.95   $99.00  
  Purchase #3 $108.91   13.272%   $123.3645   $123.36   $123.35   $123.40  
  Purchase #4 $209.88   10.706%   $232.3498   $232.35   $232.35   $232.30  
  Purchase #5 $137.40   11.242%   $152.8465   $152.85   $152.85   $152.80  
  Purchase #6 $47.96   7.175%   $51.4011   $51.40   $51.40   $51.40  
  Purchase #7 $144.93   5.599%   $153.0446   $153.04   $153.05   $153.00  
  7 purchase totals = $814.85       $887.2405   $887.23   $887.25   $887.20