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 $61.39   7.182%   $65.799   $65.80   $65.80   $65.80  
  Purchase #2 $92.26   10.274%   $101.7388   $101.74   $101.75   $101.70  
  Purchase #3 $142.31   5.243%   $149.7713   $149.77   $149.75   $149.80  
  Purchase #4 $37.27   9.815%   $40.9281   $40.93   $40.95   $40.90  
  Purchase #5 $198.89   12.328%   $223.4092   $223.41   $223.40   $223.40  
  Purchase #6 $70.59   10.147%   $77.7528   $77.75   $77.75   $77.80  
  Purchase #7 $199.48   6.596%   $212.6377   $212.64   $212.65   $212.60  
  7 purchase totals = $802.19       $872.0369   $872.04   $872.05   $872.00