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 $67.82   8.656%   $73.6905   $73.69   $73.70   $73.70  
  Purchase #2 $111.27   8.555%   $120.7891   $120.79   $120.80   $120.80  
  Purchase #3 $208.88   13.722%   $237.5425   $237.54   $237.55   $237.50  
  Purchase #4 $204.77   7.240%   $219.5953   $219.60   $219.60   $219.60  
  Purchase #5 $176.47   4.847%   $185.0235   $185.02   $185.00   $185.00  
  Purchase #6 $96.85   9.726%   $106.2696   $106.27   $106.25   $106.30  
  Purchase #7 $55.30   5.512%   $58.3481   $58.35   $58.35   $58.30  
  7 purchase totals = $921.36       $1,001.2586   $1,001.26   $1,001.25   $1,001.20