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 $159.43   10.747%   $176.5639   $176.56   $176.55   $176.60  
  Purchase #2 $25.51   13.614%   $28.9829   $28.98   $29.00   $29.00  
  Purchase #3 $73.73   6.559%   $78.566   $78.57   $78.55   $78.60  
  Purchase #4 $194.76   7.442%   $209.254   $209.25   $209.25   $209.30  
  Purchase #5 $56.61   11.775%   $63.2758   $63.28   $63.30   $63.30  
  Purchase #6 $221.80   10.234%   $244.499   $244.50   $244.50   $244.50  
  Purchase #7 $173.54   11.151%   $192.8914   $192.89   $192.90   $192.90  
  7 purchase totals = $905.38       $994.0330   $994.03   $994.05   $994.20