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 $183.92   13.449%   $208.6554   $208.66   $208.65   $208.70  
  Purchase #2 $144.98   5.674%   $153.2062   $153.21   $153.20   $153.20  
  Purchase #3 $13.64   9.652%   $14.9565   $14.96   $14.95   $15.00  
  Purchase #4 $195.32   4.261%   $203.6426   $203.64   $203.65   $203.60  
  Purchase #5 $144.96   4.764%   $151.8659   $151.87   $151.85   $151.90  
  Purchase #6 $181.48   8.126%   $196.2271   $196.23   $196.25   $196.20  
  Purchase #7 $200.45   3.778%   $208.023   $208.02   $208.00   $208.00  
  7 purchase totals = $1,064.75       $1,136.5767   $1,136.59   $1,136.55   $1,136.60