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 $228.87   10.326%   $252.5031   $252.50   $252.50   $252.50  
  Purchase #2 $114.59   9.615%   $125.6078   $125.61   $125.60   $125.60  
  Purchase #3 $168.81   5.128%   $177.4666   $177.47   $177.45   $177.50  
  Purchase #4 $209.58   8.313%   $227.0024   $227.00   $227.00   $227.00  
  Purchase #5 $186.81   3.774%   $193.8602   $193.86   $193.85   $193.90  
  Purchase #6 $152.29   5.693%   $160.9599   $160.96   $160.95   $161.00  
  Purchase #7 $56.56   3.572%   $58.5803   $58.58   $58.60   $58.60  
  7 purchase totals = $1,117.51       $1,195.9803   $1,195.98   $1,195.95   $1,196.10