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 $44.48   11.443%   $49.5698   $49.57   $49.55   $49.60  
  Purchase #2 $240.52   9.348%   $263.0038   $263.00   $263.00   $263.00  
  Purchase #3 $38.33   5.486%   $40.4328   $40.43   $40.45   $40.40  
  Purchase #4 $237.73   13.594%   $270.047   $270.05   $270.05   $270.00  
  Purchase #5 $50.93   4.125%   $53.0309   $53.03   $53.05   $53.00  
  Purchase #6 $14.42   13.317%   $16.3403   $16.34   $16.35   $16.30  
  Purchase #7 $135.87   6.602%   $144.8401   $144.84   $144.85   $144.80  
  7 purchase totals = $762.28       $837.2647   $837.26   $837.30   $837.10