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 $241.68   10.519%   $267.1023   $267.10   $267.10   $267.10  
  Purchase #2 $17.93   9.631%   $19.6568   $19.66   $19.65   $19.70  
  Purchase #3 $139.88   9.348%   $152.956   $152.96   $152.95   $153.00  
  Purchase #4 $232.90   10.267%   $256.8118   $256.81   $256.80   $256.80  
  Purchase #5 $84.63   10.211%   $93.2716   $93.27   $93.25   $93.30  
  Purchase #6 $148.52   7.731%   $160.0021   $160.00   $160.00   $160.00  
  Purchase #7 $119.62   5.475%   $126.1692   $126.17   $126.15   $126.20  
  7 purchase totals = $985.16       $1,075.9698   $1,075.97   $1,075.90   $1,076.10