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 $116.28   13.213%   $131.6441   $131.64   $131.65   $131.60  
  Purchase #2 $223.77   6.232%   $237.7153   $237.72   $237.70   $237.70  
  Purchase #3 $141.80   4.626%   $148.3597   $148.36   $148.35   $148.40  
  Purchase #4 $232.81   8.436%   $252.4499   $252.45   $252.45   $252.40  
  Purchase #5 $151.46   11.236%   $168.478   $168.48   $168.50   $168.50  
  Purchase #6 $60.58   8.867%   $65.9516   $65.95   $65.95   $66.00  
  Purchase #7 $65.79   8.384%   $71.3058   $71.31   $71.30   $71.30  
  7 purchase totals = $992.49       $1,075.9044   $1,075.91   $1,075.90   $1,075.90