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 $238.64   6.702%   $254.6337   $254.63   $254.65   $254.60  
  Purchase #2 $209.65   11.564%   $233.8939   $233.89   $233.90   $233.90  
  Purchase #3 $72.32   10.745%   $80.0908   $80.09   $80.10   $80.10  
  Purchase #4 $180.93   4.659%   $189.3595   $189.36   $189.35   $189.40  
  Purchase #5 $12.28   6.233%   $13.0454   $13.05   $13.05   $13.00  
  Purchase #6 $219.91   5.616%   $232.2601   $232.26   $232.25   $232.30  
  Purchase #7 $60.26   13.349%   $68.3041   $68.30   $68.30   $68.30  
  7 purchase totals = $993.99       $1,071.5875   $1,071.58   $1,071.60   $1,071.60