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 $57.96   6.193%   $61.5495   $61.55   $61.55   $61.50  
  Purchase #2 $80.47   5.358%   $84.7816   $84.78   $84.80   $84.80  
  Purchase #3 $229.72   3.509%   $237.7809   $237.78   $237.80   $237.80  
  Purchase #4 $96.91   12.185%   $108.7185   $108.72   $108.70   $108.70  
  Purchase #5 $128.88   4.673%   $134.9026   $134.90   $134.90   $134.90  
  Purchase #6 $213.62   3.631%   $221.3765   $221.38   $221.40   $221.40  
  Purchase #7 $219.25   6.582%   $233.681   $233.68   $233.70   $233.70  
  7 purchase totals = $1,026.81       $1,082.7906   $1,082.79   $1,082.85   $1,082.80