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 $116.59   5.772%   $123.3196   $123.32   $123.30   $123.30  
  Purchase #2 $52.26   6.577%   $55.6971   $55.70   $55.70   $55.70  
  Purchase #3 $125.83   7.430%   $135.1792   $135.18   $135.20   $135.20  
  Purchase #4 $188.87   8.130%   $204.2251   $204.23   $204.25   $204.20  
  Purchase #5 $155.84   4.723%   $163.2003   $163.20   $163.20   $163.20  
  Purchase #6 $189.40   5.576%   $199.9609   $199.96   $199.95   $200.00  
  Purchase #7 $118.84   13.234%   $134.5673   $134.57   $134.55   $134.60  
  7 purchase totals = $947.63       $1,016.1495   $1,016.16   $1,016.15   $1,016.20