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 $54.53   11.748%   $60.9362   $60.94   $60.95   $60.90  
  Purchase #2 $72.43   12.402%   $81.4128   $81.41   $81.40   $81.40  
  Purchase #3 $98.82   12.499%   $111.1715   $111.17   $111.15   $111.20  
  Purchase #4 $12.73   12.403%   $14.3089   $14.31   $14.30   $14.30  
  Purchase #5 $220.84   9.512%   $241.8463   $241.85   $241.85   $241.80  
  Purchase #6 $61.39   5.300%   $64.6437   $64.64   $64.65   $64.60  
  Purchase #7 $220.48   12.483%   $248.0025   $248.00   $248.00   $248.00  
  7 purchase totals = $741.22       $822.3219   $822.32   $822.30   $822.20