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 $203.96   8.385%   $221.062   $221.06   $221.05   $221.10  
  Purchase #2 $99.33   8.527%   $107.7999   $107.80   $107.80   $107.80  
  Purchase #3 $176.93   5.401%   $186.486   $186.49   $186.50   $186.50  
  Purchase #4 $196.33   3.687%   $203.5687   $203.57   $203.55   $203.60  
  Purchase #5 $193.45   13.784%   $220.1151   $220.12   $220.10   $220.10  
  Purchase #6 $32.68   7.346%   $35.0807   $35.08   $35.10   $35.10  
  Purchase #7 $131.41   3.868%   $136.4929   $136.49   $136.50   $136.50  
  7 purchase totals = $1,034.09       $1,110.6053   $1,110.61   $1,110.60   $1,110.70