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 $221.94   5.544%   $234.2444   $234.24   $234.25   $234.20  
  Purchase #2 $144.35   9.349%   $157.8453   $157.85   $157.85   $157.80  
  Purchase #3 $73.29   10.322%   $80.855   $80.86   $80.85   $80.90  
  Purchase #4 $137.91   12.586%   $155.2674   $155.27   $155.25   $155.30  
  Purchase #5 $147.53   8.745%   $160.4315   $160.43   $160.45   $160.40  
  Purchase #6 $108.45   5.318%   $114.2174   $114.22   $114.20   $114.20  
  Purchase #7 $112.74   7.251%   $120.9148   $120.91   $120.90   $120.90  
  7 purchase totals = $946.21       $1,023.7758   $1,023.78   $1,023.75   $1,023.70