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 $89.57   7.872%   $96.621   $96.62   $96.60   $96.60  
  Purchase #2 $17.57   3.511%   $18.1869   $18.19   $18.20   $18.20  
  Purchase #3 $218.40   4.207%   $227.5881   $227.59   $227.60   $227.60  
  Purchase #4 $214.44   6.675%   $228.7539   $228.75   $228.75   $228.80  
  Purchase #5 $120.62   5.371%   $127.0985   $127.10   $127.10   $127.10  
  Purchase #6 $60.72   5.649%   $64.1501   $64.15   $64.15   $64.20  
  Purchase #7 $235.52   7.540%   $253.2782   $253.28   $253.30   $253.30  
  7 purchase totals = $956.84       $1,015.6767   $1,015.68   $1,015.70   $1,015.80