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 $24.92   7.612%   $26.8169   $26.82   $26.80   $26.80  
  Purchase #2 $212.53   13.534%   $241.2938   $241.29   $241.30   $241.30  
  Purchase #3 $64.31   8.307%   $69.6522   $69.65   $69.65   $69.70  
  Purchase #4 $44.26   5.864%   $46.8554   $46.86   $46.85   $46.90  
  Purchase #5 $170.67   9.696%   $187.2182   $187.22   $187.20   $187.20  
  Purchase #6 $250.91   12.174%   $281.4558   $281.46   $281.45   $281.50  
  Purchase #7 $122.89   7.437%   $132.0293   $132.03   $132.05   $132.00  
  7 purchase totals = $890.49       $985.3216   $985.33   $985.30   $985.40