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 $143.79   8.844%   $156.5068   $156.51   $156.50   $156.50  
  Purchase #2 $232.55   12.449%   $261.5001   $261.50   $261.50   $261.50  
  Purchase #3 $204.97   11.528%   $228.5989   $228.60   $228.60   $228.60  
  Purchase #4 $212.41   6.194%   $225.5667   $225.57   $225.55   $225.60  
  Purchase #5 $58.40   3.752%   $60.5912   $60.59   $60.60   $60.60  
  Purchase #6 $208.50   11.294%   $232.048   $232.05   $232.05   $232.00  
  Purchase #7 $10.28   5.102%   $10.8045   $10.80   $10.80   $10.80  
  7 purchase totals = $1,070.90       $1,175.6162   $1,175.62   $1,175.60   $1,175.60