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 $205.91   6.613%   $219.5268   $219.53   $219.55   $219.50  
  Purchase #2 $118.67   4.778%   $124.3401   $124.34   $124.35   $124.30  
  Purchase #3 $215.35   4.716%   $225.5059   $225.51   $225.50   $225.50  
  Purchase #4 $214.93   9.743%   $235.8706   $235.87   $235.85   $235.90  
  Purchase #5 $11.46   11.850%   $12.818   $12.82   $12.80   $12.80  
  Purchase #6 $110.51   6.495%   $117.6876   $117.69   $117.70   $117.70  
  Purchase #7 $242.83   11.371%   $270.4422   $270.44   $270.45   $270.40  
  7 purchase totals = $1,119.66       $1,206.1912   $1,206.20   $1,206.20   $1,206.10