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 $245.67   10.452%   $271.3474   $271.35   $271.35   $271.30  
  Purchase #2 $102.42   9.271%   $111.9154   $111.92   $111.90   $111.90  
  Purchase #3 $218.66   8.147%   $236.4742   $236.47   $236.45   $236.50  
  Purchase #4 $7.86   9.844%   $8.6337   $8.63   $8.65   $8.60  
  Purchase #5 $231.84   13.480%   $263.092   $263.09   $263.10   $263.10  
  Purchase #6 $84.25   10.817%   $93.3633   $93.36   $93.35   $93.40  
  Purchase #7 $56.57   6.602%   $60.3048   $60.30   $60.30   $60.30  
  7 purchase totals = $947.27       $1,045.1308   $1,045.12   $1,045.10   $1,045.10