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 $194.78   6.275%   $207.0024   $207.00   $207.00   $207.00  
  Purchase #2 $14.95   12.289%   $16.7872   $16.79   $16.80   $16.80  
  Purchase #3 $61.47   7.625%   $66.1571   $66.16   $66.15   $66.20  
  Purchase #4 $10.58   13.811%   $12.0412   $12.04   $12.05   $12.00  
  Purchase #5 $42.42   5.447%   $44.7306   $44.73   $44.75   $44.70  
  Purchase #6 $196.47   12.819%   $221.6555   $221.66   $221.65   $221.70  
  Purchase #7 $53.30   6.379%   $56.7   $56.70   $56.70   $56.70  
  7 purchase totals = $573.97       $625.0740   $625.08   $625.10   $625.10