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 $64.84   8.711%   $70.4882   $70.49   $70.50   $70.50  
  Purchase #2 $212.80   10.747%   $235.6696   $235.67   $235.65   $235.70  
  Purchase #3 $241.81   9.227%   $264.1218   $264.12   $264.10   $264.10  
  Purchase #4 $67.27   9.858%   $73.9015   $73.90   $73.90   $73.90  
  Purchase #5 $150.58   5.328%   $158.6029   $158.60   $158.60   $158.60  
  Purchase #6 $238.81   4.688%   $250.0054   $250.01   $250.00   $250.00  
  Purchase #7 $30.64   12.418%   $34.4449   $34.44   $34.45   $34.40  
  7 purchase totals = $1,006.75       $1,087.2343   $1,087.23   $1,087.20   $1,087.20