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 $206.97   6.832%   $221.1102   $221.11   $221.10   $221.10  
  Purchase #2 $176.74   4.414%   $184.5413   $184.54   $184.55   $184.50  
  Purchase #3 $231.54   8.176%   $250.4707   $250.47   $250.45   $250.50  
  Purchase #4 $27.81   6.363%   $29.5796   $29.58   $29.60   $29.60  
  Purchase #5 $82.40   3.159%   $85.003   $85.00   $85.00   $85.00  
  Purchase #6 $193.78   6.236%   $205.8641   $205.86   $205.85   $205.90  
  Purchase #7 $71.69   8.175%   $77.5507   $77.55   $77.55   $77.60  
  7 purchase totals = $990.93       $1,054.1196   $1,054.11   $1,054.10   $1,054.20