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 $210.52   10.512%   $232.6499   $232.65   $232.65   $232.60  
  Purchase #2 $188.88   3.489%   $195.47   $195.47   $195.45   $195.50  
  Purchase #3 $27.80   10.398%   $30.6906   $30.69   $30.70   $30.70  
  Purchase #4 $120.33   9.161%   $131.3534   $131.35   $131.35   $131.40  
  Purchase #5 $168.27   12.830%   $189.859   $189.86   $189.85   $189.90  
  Purchase #6 $175.69   4.250%   $183.1568   $183.16   $183.15   $183.20  
  Purchase #7 $59.85   10.125%   $65.9098   $65.91   $65.90   $65.90  
  7 purchase totals = $951.34       $1,029.0895   $1,029.09   $1,029.05   $1,029.20