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 $125.84   13.129%   $142.3615   $142.36   $142.35   $142.40  
  Purchase #2 $228.62   10.205%   $251.9507   $251.95   $251.95   $252.00  
  Purchase #3 $245.51   6.193%   $260.7144   $260.71   $260.70   $260.70  
  Purchase #4 $177.94   9.523%   $194.8852   $194.89   $194.90   $194.90  
  Purchase #5 $47.76   6.428%   $50.83   $50.83   $50.85   $50.80  
  Purchase #6 $192.72   7.747%   $207.65   $207.65   $207.65   $207.70  
  Purchase #7 $173.83   10.553%   $192.1743   $192.17   $192.15   $192.20  
  7 purchase totals = $1,192.22       $1,300.5661   $1,300.56   $1,300.55   $1,300.70