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 $92.58   4.696%   $96.9276   $96.93   $96.95   $96.90  
  Purchase #2 $245.83   5.361%   $259.0089   $259.01   $259.00   $259.00  
  Purchase #3 $215.99   9.182%   $235.8222   $235.82   $235.80   $235.80  
  Purchase #4 $182.48   5.233%   $192.0292   $192.03   $192.05   $192.00  
  Purchase #5 $119.92   6.460%   $127.6668   $127.67   $127.65   $127.70  
  Purchase #6 $120.84   5.437%   $127.4101   $127.41   $127.40   $127.40  
  Purchase #7 $128.39   9.820%   $140.9979   $141.00   $141.00   $141.00  
  7 purchase totals = $1,106.03       $1,179.8627   $1,179.87   $1,179.85   $1,179.80