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 $198.55   9.751%   $217.9106   $217.91   $217.90   $217.90  
  Purchase #2 $157.92   13.116%   $178.6328   $178.63   $178.65   $178.60  
  Purchase #3 $46.56   13.512%   $52.8512   $52.85   $52.85   $52.90  
  Purchase #4 $201.41   3.708%   $208.8783   $208.88   $208.90   $208.90  
  Purchase #5 $182.94   10.591%   $202.3152   $202.32   $202.30   $202.30  
  Purchase #6 $239.60   11.622%   $267.4463   $267.45   $267.45   $267.40  
  Purchase #7 $214.57   13.395%   $243.3117   $243.31   $243.30   $243.30  
  7 purchase totals = $1,241.55       $1,371.3461   $1,371.35   $1,371.35   $1,371.30