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 $212.98   4.703%   $222.9964   $223.00   $223.00   $223.00  
  Purchase #2 $62.71   11.449%   $69.8897   $69.89   $69.90   $69.90  
  Purchase #3 $33.51   13.522%   $38.0412   $38.04   $38.05   $38.00  
  Purchase #4 $86.56   5.542%   $91.3572   $91.36   $91.35   $91.40  
  Purchase #5 $155.59   10.743%   $172.305   $172.31   $172.30   $172.30  
  Purchase #6 $129.92   10.600%   $143.6915   $143.69   $143.70   $143.70  
  Purchase #7 $206.68   10.450%   $228.2781   $228.28   $228.30   $228.30  
  7 purchase totals = $887.95       $966.5591   $966.57   $966.60   $966.60