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 $169.59   8.353%   $183.7559   $183.76   $183.75   $183.80  
  Purchase #2 $121.77   9.227%   $133.0057   $133.01   $133.00   $133.00  
  Purchase #3 $207.28   13.736%   $235.752   $235.75   $235.75   $235.80  
  Purchase #4 $93.62   13.682%   $106.4291   $106.43   $106.45   $106.40  
  Purchase #5 $137.67   8.671%   $149.6074   $149.61   $149.60   $149.60  
  Purchase #6 $53.39   11.794%   $59.6868   $59.69   $59.70   $59.70  
  Purchase #7 $46.29   5.291%   $48.7392   $48.74   $48.75   $48.70  
  7 purchase totals = $829.61       $916.9761   $916.99   $917.00   $917.00