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 $201.26   13.591%   $228.6132   $228.61   $228.60   $228.60  
  Purchase #2 $171.45   12.641%   $193.123   $193.12   $193.10   $193.10  
  Purchase #3 $5.74   11.244%   $6.3854   $6.39   $6.40   $6.40  
  Purchase #4 $248.82   8.431%   $269.798   $269.80   $269.80   $269.80  
  Purchase #5 $113.34   5.456%   $119.5238   $119.52   $119.50   $119.50  
  Purchase #6 $238.34   3.507%   $246.6986   $246.70   $246.70   $246.70  
  Purchase #7 $37.39   8.815%   $40.6859   $40.69   $40.70   $40.70  
  7 purchase totals = $1,016.34       $1,104.8279   $1,104.83   $1,104.80   $1,104.80