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 $53.45   5.634%   $56.4614   $56.46   $56.45   $56.50  
  Purchase #2 $104.69   8.873%   $113.9791   $113.98   $114.00   $114.00  
  Purchase #3 $204.70   10.311%   $225.8066   $225.81   $225.80   $225.80  
  Purchase #4 $116.84   6.692%   $124.6589   $124.66   $124.65   $124.70  
  Purchase #5 $76.81   3.830%   $79.7518   $79.75   $79.75   $79.80  
  Purchase #6 $87.34   4.753%   $91.4913   $91.49   $91.50   $91.50  
  Purchase #7 $193.33   7.437%   $207.708   $207.71   $207.70   $207.70  
  7 purchase totals = $837.16       $899.8571   $899.86   $899.85   $900.00