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 $238.52   5.871%   $252.5235   $252.52   $252.50   $252.50  
  Purchase #2 $54.91   9.868%   $60.3285   $60.33   $60.35   $60.30  
  Purchase #3 $159.48   6.794%   $170.3151   $170.32   $170.30   $170.30  
  Purchase #4 $31.27   8.493%   $33.9258   $33.93   $33.95   $33.90  
  Purchase #5 $209.74   13.177%   $237.3774   $237.38   $237.40   $237.40  
  Purchase #6 $168.35   8.355%   $182.4156   $182.42   $182.40   $182.40  
  Purchase #7 $132.38   4.826%   $138.7687   $138.77   $138.75   $138.80  
  7 purchase totals = $994.65       $1,075.6546   $1,075.67   $1,075.65   $1,075.60