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 $182.72   11.539%   $203.8041   $203.80   $203.80   $203.80  
  Purchase #2 $43.46   9.871%   $47.7499   $47.75   $47.75   $47.70  
  Purchase #3 $62.64   3.540%   $64.8575   $64.86   $64.85   $64.90  
  Purchase #4 $37.75   13.245%   $42.75   $42.75   $42.75   $42.80  
  Purchase #5 $106.66   10.207%   $117.5468   $117.55   $117.55   $117.50  
  Purchase #6 $33.60   11.850%   $37.5816   $37.58   $37.60   $37.60  
  Purchase #7 $211.60   4.575%   $221.2807   $221.28   $221.30   $221.30  
  7 purchase totals = $678.43       $735.5706   $735.57   $735.60   $735.60