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 $217.91   5.817%   $230.5858   $230.59   $230.60   $230.60  
  Purchase #2 $43.73   5.357%   $46.0726   $46.07   $46.05   $46.10  
  Purchase #3 $89.96   4.826%   $94.3015   $94.30   $94.30   $94.30  
  Purchase #4 $232.58   13.210%   $263.3038   $263.30   $263.30   $263.30  
  Purchase #5 $146.95   12.853%   $165.8375   $165.84   $165.85   $165.80  
  Purchase #6 $216.57   13.511%   $245.8308   $245.83   $245.85   $245.80  
  Purchase #7 $195.46   10.209%   $215.4145   $215.41   $215.40   $215.40  
  7 purchase totals = $1,143.16       $1,261.3465   $1,261.34   $1,261.35   $1,261.30