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 $60.47   11.130%   $67.2003   $67.20   $67.20   $67.20  
  Purchase #2 $142.89   12.800%   $161.1799   $161.18   $161.20   $161.20  
  Purchase #3 $227.64   10.843%   $252.323   $252.32   $252.30   $252.30  
  Purchase #4 $182.42   11.665%   $203.6993   $203.70   $203.70   $203.70  
  Purchase #5 $52.35   9.588%   $57.3693   $57.37   $57.35   $57.40  
  Purchase #6 $233.53   3.417%   $241.5097   $241.51   $241.50   $241.50  
  Purchase #7 $74.99   10.637%   $82.9667   $82.97   $82.95   $83.00  
  7 purchase totals = $974.29       $1,066.2482   $1,066.25   $1,066.20   $1,066.30