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 $236.61   7.601%   $254.5947   $254.59   $254.60   $254.60  
  Purchase #2 $164.81   5.747%   $174.2816   $174.28   $174.30   $174.30  
  Purchase #3 $243.45   9.625%   $266.8821   $266.88   $266.90   $266.90  
  Purchase #4 $234.44   5.173%   $246.5676   $246.57   $246.55   $246.60  
  Purchase #5 $111.64   8.599%   $121.2399   $121.24   $121.25   $121.20  
  Purchase #6 $110.72   12.560%   $124.6264   $124.63   $124.65   $124.60  
  Purchase #7 $88.43   4.291%   $92.2245   $92.22   $92.20   $92.20  
  7 purchase totals = $1,190.10       $1,280.4168   $1,280.41   $1,280.45   $1,280.40