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 $134.61   12.532%   $151.4793   $151.48   $151.50   $151.50  
  Purchase #2 $219.85   13.263%   $249.0087   $249.01   $249.00   $249.00  
  Purchase #3 $66.47   4.131%   $69.2159   $69.22   $69.20   $69.20  
  Purchase #4 $165.33   12.763%   $186.4311   $186.43   $186.45   $186.40  
  Purchase #5 $140.29   12.641%   $158.0241   $158.02   $158.00   $158.00  
  Purchase #6 $132.53   6.656%   $141.3512   $141.35   $141.35   $141.40  
  Purchase #7 $164.28   13.222%   $186.0011   $186.00   $186.00   $186.00  
  7 purchase totals = $1,023.36       $1,141.5114   $1,141.51   $1,141.50   $1,141.50