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 $39.60   3.389%   $40.942   $40.94   $40.95   $40.90  
  Purchase #2 $150.27   4.529%   $157.0757   $157.08   $157.10   $157.10  
  Purchase #3 $214.46   8.343%   $232.3524   $232.35   $232.35   $232.40  
  Purchase #4 $232.83   10.364%   $256.9605   $256.96   $256.95   $257.00  
  Purchase #5 $54.77   9.600%   $60.0279   $60.03   $60.05   $60.00  
  Purchase #6 $84.25   7.506%   $90.5738   $90.57   $90.55   $90.60  
  Purchase #7 $18.55   10.609%   $20.518   $20.52   $20.50   $20.50  
  7 purchase totals = $794.73       $858.4503   $858.45   $858.45   $858.50