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 $248.82   13.266%   $281.8285   $281.83   $281.85   $281.80  
  Purchase #2 $95.43   11.810%   $106.7003   $106.70   $106.70   $106.70  
  Purchase #3 $23.46   5.367%   $24.7191   $24.72   $24.70   $24.70  
  Purchase #4 $27.92   13.722%   $31.7512   $31.75   $31.75   $31.80  
  Purchase #5 $184.89   13.307%   $209.4933   $209.49   $209.50   $209.50  
  Purchase #6 $60.92   10.634%   $67.3982   $67.40   $67.40   $67.40  
  Purchase #7 $216.61   10.843%   $240.097   $240.10   $240.10   $240.10  
  7 purchase totals = $858.05       $961.9876   $961.99   $962.00   $962.00