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 $95.41   3.305%   $98.5633   $98.56   $98.55   $98.60  
  Purchase #2 $113.69   11.707%   $126.9997   $127.00   $127.00   $127.00  
  Purchase #3 $167.85   4.388%   $175.2153   $175.22   $175.20   $175.20  
  Purchase #4 $103.30   11.552%   $115.2332   $115.23   $115.25   $115.20  
  Purchase #5 $63.59   10.654%   $70.3649   $70.36   $70.35   $70.40  
  Purchase #6 $169.65   5.280%   $178.6075   $178.61   $178.60   $178.60  
  Purchase #7 $76.71   9.689%   $84.1424   $84.14   $84.15   $84.10  
  7 purchase totals = $790.20       $849.1263   $849.12   $849.10   $849.10