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 $5.46   4.145%   $5.6863   $5.69   $5.70   $5.70  
  Purchase #2 $243.97   7.366%   $261.9408   $261.94   $261.95   $261.90  
  Purchase #3 $231.79   12.847%   $261.5681   $261.57   $261.55   $261.60  
  Purchase #4 $142.98   8.321%   $154.8774   $154.88   $154.90   $154.90  
  Purchase #5 $93.26   9.590%   $102.2036   $102.20   $102.20   $102.20  
  Purchase #6 $136.51   3.245%   $140.9397   $140.94   $140.95   $140.90  
  Purchase #7 $48.25   10.449%   $53.2916   $53.29   $53.30   $53.30  
  7 purchase totals = $902.22       $980.5075   $980.51   $980.55   $980.50