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 $207.51   6.483%   $220.9629   $220.96   $220.95   $221.00  
  Purchase #2 $249.57   11.461%   $278.1732   $278.17   $278.15   $278.20  
  Purchase #3 $63.38   13.348%   $71.84   $71.84   $71.85   $71.80  
  Purchase #4 $164.51   10.620%   $181.981   $181.98   $182.00   $182.00  
  Purchase #5 $9.37   3.413%   $9.6898   $9.69   $9.70   $9.70  
  Purchase #6 $128.25   10.154%   $141.2725   $141.27   $141.25   $141.30  
  Purchase #7 $101.30   8.872%   $110.2873   $110.29   $110.30   $110.30  
  7 purchase totals = $923.89       $1,014.2067   $1,014.20   $1,014.20   $1,014.30