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 $232.68   8.390%   $252.2019   $252.20   $252.20   $252.20  
  Purchase #2 $113.88   3.295%   $117.6323   $117.63   $117.65   $117.60  
  Purchase #3 $151.33   11.122%   $168.1609   $168.16   $168.15   $168.20  
  Purchase #4 $93.38   6.555%   $99.5011   $99.50   $99.50   $99.50  
  Purchase #5 $174.42   8.835%   $189.83   $189.83   $189.85   $189.80  
  Purchase #6 $6.90   11.673%   $7.7054   $7.71   $7.70   $7.70  
  Purchase #7 $223.76   7.613%   $240.7948   $240.79   $240.80   $240.80  
  7 purchase totals = $996.35       $1,075.8264   $1,075.82   $1,075.85   $1,075.80