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 $145.31   6.504%   $154.761   $154.76   $154.75   $154.80  
  Purchase #2 $65.75   7.797%   $70.8765   $70.88   $70.90   $70.90  
  Purchase #3 $77.86   3.363%   $80.4784   $80.48   $80.50   $80.50  
  Purchase #4 $200.30   13.137%   $226.6134   $226.61   $226.60   $226.60  
  Purchase #5 $27.50   12.362%   $30.8996   $30.90   $30.90   $30.90  
  Purchase #6 $245.46   9.307%   $268.305   $268.31   $268.30   $268.30  
  Purchase #7 $62.77   4.833%   $65.8037   $65.80   $65.80   $65.80  
  7 purchase totals = $824.95       $897.7376   $897.74   $897.75   $897.80