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 $186.95   13.722%   $212.6033   $212.60   $212.60   $212.60  
  Purchase #2 $54.97   6.597%   $58.5964   $58.60   $58.60   $58.60  
  Purchase #3 $157.89   8.416%   $171.178   $171.18   $171.20   $171.20  
  Purchase #4 $156.28   4.257%   $162.9328   $162.93   $162.95   $162.90  
  Purchase #5 $246.52   10.791%   $273.122   $273.12   $273.10   $273.10  
  Purchase #6 $34.71   10.859%   $38.4792   $38.48   $38.50   $38.50  
  Purchase #7 $109.45   4.725%   $114.6215   $114.62   $114.60   $114.60  
  7 purchase totals = $946.77       $1,031.5332   $1,031.53   $1,031.55   $1,031.50