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 $248.68   5.533%   $262.4395   $262.44   $262.45   $262.40  
  Purchase #2 $29.93   10.471%   $33.064   $33.06   $33.05   $33.10  
  Purchase #3 $194.41   11.348%   $216.4716   $216.47   $216.45   $216.50  
  Purchase #4 $150.29   13.529%   $170.6227   $170.62   $170.60   $170.60  
  Purchase #5 $205.71   7.778%   $221.7101   $221.71   $221.70   $221.70  
  Purchase #6 $52.34   3.834%   $54.3467   $54.35   $54.35   $54.30  
  Purchase #7 $131.99   3.444%   $136.5357   $136.54   $136.55   $136.50  
  7 purchase totals = $1,013.35       $1,095.1903   $1,095.19   $1,095.15   $1,095.10