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 $104.74   9.131%   $114.3038   $114.30   $114.30   $114.30  
  Purchase #2 $135.57   11.198%   $150.7511   $150.75   $150.75   $150.80  
  Purchase #3 $181.82   13.786%   $206.8857   $206.89   $206.90   $206.90  
  Purchase #4 $235.35   9.585%   $257.9083   $257.91   $257.90   $257.90  
  Purchase #5 $60.62   5.629%   $64.0323   $64.03   $64.05   $64.00  
  Purchase #6 $130.88   4.633%   $136.9437   $136.94   $136.95   $136.90  
  Purchase #7 $69.82   4.401%   $72.8928   $72.89   $72.90   $72.90  
  7 purchase totals = $918.80       $1,003.7177   $1,003.71   $1,003.75   $1,003.70