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 $207.65   3.190%   $214.274   $214.27   $214.25   $214.30  
  Purchase #2 $64.45   9.560%   $70.6114   $70.61   $70.60   $70.60  
  Purchase #3 $110.99   10.107%   $122.2078   $122.21   $122.20   $122.20  
  Purchase #4 $98.32   4.794%   $103.0335   $103.03   $103.05   $103.00  
  Purchase #5 $76.65   13.848%   $87.2645   $87.26   $87.25   $87.30  
  Purchase #6 $158.71   5.530%   $167.4867   $167.49   $167.50   $167.50  
  Purchase #7 $6.89   6.112%   $7.3111   $7.31   $7.30   $7.30  
  7 purchase totals = $723.66       $772.1890   $772.18   $772.15   $772.20