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 $208.48   5.856%   $220.6886   $220.69   $220.70   $220.70  
  Purchase #2 $126.83   6.317%   $134.8419   $134.84   $134.85   $134.80  
  Purchase #3 $102.42   3.272%   $105.7712   $105.77   $105.75   $105.80  
  Purchase #4 $23.80   4.166%   $24.7915   $24.79   $24.80   $24.80  
  Purchase #5 $136.33   5.558%   $143.9072   $143.91   $143.90   $143.90  
  Purchase #6 $202.54   8.214%   $219.1766   $219.18   $219.20   $219.20  
  Purchase #7 $161.76   10.476%   $178.706   $178.71   $178.70   $178.70  
  7 purchase totals = $962.16       $1,027.8830   $1,027.89   $1,027.90   $1,027.90