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 $56.70   12.726%   $63.9156   $63.92   $63.90   $63.90  
  Purchase #2 $211.91   9.801%   $232.6793   $232.68   $232.70   $232.70  
  Purchase #3 $88.99   5.437%   $93.8284   $93.83   $93.85   $93.80  
  Purchase #4 $206.43   13.432%   $234.1577   $234.16   $234.15   $234.20  
  Purchase #5 $249.28   11.443%   $277.8051   $277.81   $277.80   $277.80  
  Purchase #6 $110.37   3.569%   $114.3091   $114.31   $114.30   $114.30  
  Purchase #7 $28.87   7.835%   $31.132   $31.13   $31.15   $31.10  
  7 purchase totals = $952.55       $1,047.8272   $1,047.84   $1,047.85   $1,047.80