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 $218.85   11.394%   $243.7858   $243.79   $243.80   $243.80  
  Purchase #2 $59.43   8.839%   $64.683   $64.68   $64.70   $64.70  
  Purchase #3 $71.88   8.386%   $77.9079   $77.91   $77.90   $77.90  
  Purchase #4 $114.72   10.534%   $126.8046   $126.80   $126.80   $126.80  
  Purchase #5 $156.49   12.212%   $175.6006   $175.60   $175.60   $175.60  
  Purchase #6 $113.93   3.230%   $117.6099   $117.61   $117.60   $117.60  
  Purchase #7 $226.55   9.685%   $248.4914   $248.49   $248.50   $248.50  
  7 purchase totals = $961.85       $1,054.8832   $1,054.88   $1,054.90   $1,054.90