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 $215.58   13.322%   $244.2996   $244.30   $244.30   $244.30  
  Purchase #2 $24.42   9.249%   $26.6786   $26.68   $26.70   $26.70  
  Purchase #3 $241.43   4.277%   $251.756   $251.76   $251.75   $251.80  
  Purchase #4 $230.28   10.695%   $254.9084   $254.91   $254.90   $254.90  
  Purchase #5 $222.28   8.572%   $241.3338   $241.33   $241.35   $241.30  
  Purchase #6 $87.88   5.471%   $92.6879   $92.69   $92.70   $92.70  
  Purchase #7 $49.97   8.483%   $54.209   $54.21   $54.20   $54.20  
  7 purchase totals = $1,071.84       $1,165.8733   $1,165.88   $1,165.90   $1,165.90