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 $185.26   11.712%   $206.9577   $206.96   $206.95   $207.00  
  Purchase #2 $156.64   4.204%   $163.2251   $163.23   $163.25   $163.20  
  Purchase #3 $19.76   8.348%   $21.4096   $21.41   $21.40   $21.40  
  Purchase #4 $103.32   4.782%   $108.2608   $108.26   $108.25   $108.30  
  Purchase #5 $136.71   9.283%   $149.4008   $149.40   $149.40   $149.40  
  Purchase #6 $28.58   8.325%   $30.9593   $30.96   $30.95   $31.00  
  Purchase #7 $65.94   3.767%   $68.424   $68.42   $68.40   $68.40  
  7 purchase totals = $696.21       $748.6373   $748.64   $748.60   $748.70