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 $226.63   11.768%   $253.2998   $253.30   $253.30   $253.30  
  Purchase #2 $159.64   3.663%   $165.4876   $165.49   $165.50   $165.50  
  Purchase #3 $51.54   12.841%   $58.1583   $58.16   $58.15   $58.20  
  Purchase #4 $56.60   3.847%   $58.7774   $58.78   $58.80   $58.80  
  Purchase #5 $105.84   8.217%   $114.5369   $114.54   $114.55   $114.50  
  Purchase #6 $212.59   7.400%   $228.3217   $228.32   $228.30   $228.30  
  Purchase #7 $165.35   6.497%   $176.0928   $176.09   $176.10   $176.10  
  7 purchase totals = $978.19       $1,054.6745   $1,054.68   $1,054.70   $1,054.70