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 $169.95   4.334%   $177.3156   $177.32   $177.30   $177.30  
  Purchase #2 $48.28   11.411%   $53.7892   $53.79   $53.80   $53.80  
  Purchase #3 $221.61   9.523%   $242.7139   $242.71   $242.70   $242.70  
  Purchase #4 $116.81   9.278%   $127.6476   $127.65   $127.65   $127.60  
  Purchase #5 $153.46   8.587%   $166.6376   $166.64   $166.65   $166.60  
  Purchase #6 $41.62   11.333%   $46.3368   $46.34   $46.35   $46.30  
  Purchase #7 $245.54   9.644%   $269.2199   $269.22   $269.20   $269.20  
  7 purchase totals = $997.27       $1,083.6606   $1,083.67   $1,083.65   $1,083.50