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 $97.91   6.224%   $104.0039   $104.00   $104.00   $104.00  
  Purchase #2 $75.32   8.241%   $81.5271   $81.53   $81.55   $81.50  
  Purchase #3 $150.44   11.276%   $167.4036   $167.40   $167.40   $167.40  
  Purchase #4 $167.34   8.328%   $181.2761   $181.28   $181.30   $181.30  
  Purchase #5 $231.69   11.659%   $258.7027   $258.70   $258.70   $258.70  
  Purchase #6 $157.29   6.187%   $167.0215   $167.02   $167.00   $167.00  
  Purchase #7 $218.29   10.705%   $241.6579   $241.66   $241.65   $241.70  
  7 purchase totals = $1,098.28       $1,201.5928   $1,201.59   $1,201.60   $1,201.60