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 $204.95   5.824%   $216.8863   $216.89   $216.90   $216.90  
  Purchase #2 $133.70   7.493%   $143.7181   $143.72   $143.70   $143.70  
  Purchase #3 $100.81   3.661%   $104.5007   $104.50   $104.50   $104.50  
  Purchase #4 $14.48   11.402%   $16.131   $16.13   $16.15   $16.10  
  Purchase #5 $184.71   11.694%   $206.31   $206.31   $206.30   $206.30  
  Purchase #6 $203.64   13.233%   $230.5877   $230.59   $230.60   $230.60  
  Purchase #7 $123.54   7.237%   $132.4806   $132.48   $132.50   $132.50  
  7 purchase totals = $965.83       $1,050.6144   $1,050.62   $1,050.65   $1,050.60