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 $112.40   6.792%   $120.0342   $120.03   $120.05   $120.00  
  Purchase #2 $203.37   12.802%   $229.4054   $229.41   $229.40   $229.40  
  Purchase #3 $187.76   7.678%   $202.1762   $202.18   $202.20   $202.20  
  Purchase #4 $164.95   7.318%   $177.021   $177.02   $177.00   $177.00  
  Purchase #5 $24.28   11.805%   $27.1463   $27.15   $27.15   $27.10  
  Purchase #6 $163.60   12.498%   $184.0467   $184.05   $184.05   $184.00  
  Purchase #7 $239.66   11.537%   $267.3096   $267.31   $267.30   $267.30  
  7 purchase totals = $1,096.02       $1,207.1394   $1,207.15   $1,207.15   $1,207.00