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 $210.92   5.866%   $223.2926   $223.29   $223.30   $223.30  
  Purchase #2 $207.71   11.721%   $232.0557   $232.06   $232.05   $232.10  
  Purchase #3 $12.85   13.365%   $14.5674   $14.57   $14.55   $14.60  
  Purchase #4 $225.31   3.307%   $232.761   $232.76   $232.75   $232.80  
  Purchase #5 $160.84   4.760%   $168.496   $168.50   $168.50   $168.50  
  Purchase #6 $21.29   9.252%   $23.2598   $23.26   $23.25   $23.30  
  Purchase #7 $169.69   7.873%   $183.0497   $183.05   $183.05   $183.00  
  7 purchase totals = $1,008.61       $1,077.4822   $1,077.49   $1,077.45   $1,077.60