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 $249.37   7.790%   $268.7959   $268.80   $268.80   $268.80  
  Purchase #2 $90.38   5.816%   $95.6365   $95.64   $95.65   $95.60  
  Purchase #3 $23.64   8.259%   $25.5924   $25.59   $25.60   $25.60  
  Purchase #4 $219.26   10.209%   $241.6443   $241.64   $241.65   $241.60  
  Purchase #5 $101.53   3.264%   $104.8439   $104.84   $104.85   $104.80  
  Purchase #6 $246.85   11.290%   $274.7194   $274.72   $274.70   $274.70  
  Purchase #7 $24.36   7.364%   $26.1539   $26.15   $26.15   $26.20  
  7 purchase totals = $955.39       $1,037.3863   $1,037.38   $1,037.40   $1,037.30