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 $111.44   11.621%   $124.3904   $124.39   $124.40   $124.40  
  Purchase #2 $216.48   6.102%   $229.6896   $229.69   $229.70   $229.70  
  Purchase #3 $61.71   12.712%   $69.5546   $69.55   $69.55   $69.60  
  Purchase #4 $190.96   13.871%   $217.4481   $217.45   $217.45   $217.40  
  Purchase #5 $243.67   13.599%   $276.8067   $276.81   $276.80   $276.80  
  Purchase #6 $61.94   11.362%   $68.9776   $68.98   $69.00   $69.00  
  Purchase #7 $157.90   5.166%   $166.0571   $166.06   $166.05   $166.10  
  7 purchase totals = $1,044.10       $1,152.9241   $1,152.93   $1,152.95   $1,153.00