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 $61.99   13.826%   $70.5607   $70.56   $70.55   $70.60  
  Purchase #2 $246.29   4.593%   $257.6021   $257.60   $257.60   $257.60  
  Purchase #3 $115.42   3.444%   $119.3951   $119.40   $119.40   $119.40  
  Purchase #4 $172.99   7.398%   $185.7878   $185.79   $185.80   $185.80  
  Purchase #5 $93.50   9.867%   $102.7256   $102.73   $102.75   $102.70  
  Purchase #6 $136.74   9.528%   $149.7686   $149.77   $149.75   $149.80  
  Purchase #7 $9.54   10.113%   $10.5048   $10.50   $10.50   $10.50  
  7 purchase totals = $836.47       $896.3447   $896.35   $896.35   $896.40