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 $238.43   10.527%   $263.5295   $263.53   $263.55   $263.50  
  Purchase #2 $192.68   5.780%   $203.8169   $203.82   $203.80   $203.80  
  Purchase #3 $11.61   12.320%   $13.0404   $13.04   $13.05   $13.00  
  Purchase #4 $142.99   9.635%   $156.7671   $156.77   $156.75   $156.80  
  Purchase #5 $78.84   12.585%   $88.762   $88.76   $88.75   $88.80  
  Purchase #6 $232.40   3.787%   $241.201   $241.20   $241.20   $241.20  
  Purchase #7 $113.98   3.759%   $118.2645   $118.26   $118.25   $118.30  
  7 purchase totals = $1,010.93       $1,085.3814   $1,085.38   $1,085.35   $1,085.40