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 $186.85   13.732%   $212.5082   $212.51   $212.50   $212.50  
  Purchase #2 $244.77   9.612%   $268.2973   $268.30   $268.30   $268.30  
  Purchase #3 $153.84   9.471%   $168.4102   $168.41   $168.40   $168.40  
  Purchase #4 $90.81   11.359%   $101.1251   $101.13   $101.15   $101.10  
  Purchase #5 $250.80   10.241%   $276.4844   $276.48   $276.50   $276.50  
  Purchase #6 $23.68   7.565%   $25.4714   $25.47   $25.45   $25.50  
  Purchase #7 $6.80   13.512%   $7.7188   $7.72   $7.70   $7.70  
  7 purchase totals = $957.55       $1,060.0154   $1,060.02   $1,060.00   $1,060.00