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 $201.89   12.687%   $227.5038   $227.50   $227.50   $227.50  
  Purchase #2 $90.79   3.726%   $94.1728   $94.17   $94.15   $94.20  
  Purchase #3 $115.53   4.457%   $120.6792   $120.68   $120.70   $120.70  
  Purchase #4 $33.70   4.748%   $35.3001   $35.30   $35.30   $35.30  
  Purchase #5 $197.38   3.108%   $203.5146   $203.51   $203.50   $203.50  
  Purchase #6 $214.51   3.416%   $221.8377   $221.84   $221.85   $221.80  
  Purchase #7 $86.41   5.530%   $91.1885   $91.19   $91.20   $91.20  
  7 purchase totals = $940.21       $994.1967   $994.19   $994.20   $994.20