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 $34.31   12.371%   $38.5545   $38.55   $38.55   $38.60  
  Purchase #2 $158.30   5.266%   $166.6361   $166.64   $166.65   $166.60  
  Purchase #3 $108.52   12.314%   $121.8832   $121.88   $121.90   $121.90  
  Purchase #4 $164.77   11.732%   $184.1008   $184.10   $184.10   $184.10  
  Purchase #5 $208.51   5.335%   $219.634   $219.63   $219.65   $219.60  
  Purchase #6 $122.42   6.551%   $130.4397   $130.44   $130.45   $130.40  
  Purchase #7 $192.39   10.239%   $212.0888   $212.09   $212.10   $212.10  
  7 purchase totals = $989.22       $1,073.3371   $1,073.33   $1,073.40   $1,073.30