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 $56.32   12.146%   $63.1606   $63.16   $63.15   $63.20  
  Purchase #2 $223.71   11.312%   $249.0161   $249.02   $249.00   $249.00  
  Purchase #3 $196.89   11.194%   $218.9299   $218.93   $218.95   $218.90  
  Purchase #4 $89.38   3.481%   $92.4913   $92.49   $92.50   $92.50  
  Purchase #5 $148.29   9.232%   $161.9801   $161.98   $162.00   $162.00  
  Purchase #6 $80.66   8.592%   $87.5903   $87.59   $87.60   $87.60  
  Purchase #7 $224.50   12.379%   $252.2909   $252.29   $252.30   $252.30  
  7 purchase totals = $1,019.75       $1,125.4592   $1,125.46   $1,125.50   $1,125.50