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 $232.58   5.569%   $245.5324   $245.53   $245.55   $245.50  
  Purchase #2 $197.54   10.599%   $218.4773   $218.48   $218.50   $218.50  
  Purchase #3 $108.32   10.777%   $119.9936   $119.99   $120.00   $120.00  
  Purchase #4 $98.95   7.610%   $106.4801   $106.48   $106.50   $106.50  
  Purchase #5 $134.92   6.494%   $143.6817   $143.68   $143.70   $143.70  
  Purchase #6 $25.87   12.770%   $29.1736   $29.17   $29.15   $29.20  
  Purchase #7 $156.72   6.867%   $167.482   $167.48   $167.50   $167.50  
  7 purchase totals = $954.90       $1,030.8207   $1,030.81   $1,030.90   $1,030.90