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 $170.68   3.322%   $176.35   $176.35   $176.35   $176.40  
  Purchase #2 $5.99   8.524%   $6.5006   $6.50   $6.50   $6.50  
  Purchase #3 $172.36   12.866%   $194.5358   $194.54   $194.55   $194.50  
  Purchase #4 $65.60   10.212%   $72.2991   $72.30   $72.30   $72.30  
  Purchase #5 $213.65   5.167%   $224.6893   $224.69   $224.70   $224.70  
  Purchase #6 $200.73   5.447%   $211.6638   $211.66   $211.65   $211.70  
  Purchase #7 $129.83   13.386%   $147.209   $147.21   $147.20   $147.20  
  7 purchase totals = $958.84       $1,033.2476   $1,033.25   $1,033.25   $1,033.30