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 $53.39   5.805%   $56.4893   $56.49   $56.50   $56.50  
  Purchase #2 $248.48   10.343%   $274.1803   $274.18   $274.20   $274.20  
  Purchase #3 $171.52   3.757%   $177.964   $177.96   $177.95   $178.00  
  Purchase #4 $246.37   4.546%   $257.57   $257.57   $257.55   $257.60  
  Purchase #5 $105.65   10.752%   $117.0095   $117.01   $117.00   $117.00  
  Purchase #6 $224.37   13.335%   $254.2897   $254.29   $254.30   $254.30  
  Purchase #7 $158.75   11.667%   $177.2714   $177.27   $177.25   $177.30  
  7 purchase totals = $1,208.53       $1,314.7742   $1,314.77   $1,314.75   $1,314.90