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 $26.49   7.497%   $28.476   $28.48   $28.50   $28.50  
  Purchase #2 $111.49   6.841%   $119.117   $119.12   $119.10   $119.10  
  Purchase #3 $147.36   5.728%   $155.8008   $155.80   $155.80   $155.80  
  Purchase #4 $104.71   9.471%   $114.6271   $114.63   $114.65   $114.60  
  Purchase #5 $243.82   6.109%   $258.715   $258.72   $258.70   $258.70  
  Purchase #6 $19.66   3.759%   $20.399   $20.40   $20.40   $20.40  
  Purchase #7 $61.80   13.300%   $70.0194   $70.02   $70.00   $70.00  
  7 purchase totals = $715.33       $767.1543   $767.17   $767.15   $767.10