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 $84.28   11.783%   $94.2107   $94.21   $94.20   $94.20  
  Purchase #2 $29.26   8.696%   $31.8044   $31.80   $31.80   $31.80  
  Purchase #3 $101.28   13.236%   $114.6854   $114.69   $114.70   $114.70  
  Purchase #4 $246.53   12.194%   $276.5919   $276.59   $276.60   $276.60  
  Purchase #5 $6.57   12.239%   $7.3741   $7.37   $7.35   $7.40  
  Purchase #6 $120.76   10.119%   $132.9797   $132.98   $133.00   $133.00  
  Purchase #7 $113.29   9.851%   $124.4502   $124.45   $124.45   $124.50  
  7 purchase totals = $701.97       $782.0964   $782.09   $782.10   $782.20