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 $217.56   10.823%   $241.1065   $241.11   $241.10   $241.10  
  Purchase #2 $141.43   5.143%   $148.7037   $148.70   $148.70   $148.70  
  Purchase #3 $185.73   7.835%   $200.2819   $200.28   $200.30   $200.30  
  Purchase #4 $191.43   10.635%   $211.7886   $211.79   $211.80   $211.80  
  Purchase #5 $156.37   11.461%   $174.2916   $174.29   $174.30   $174.30  
  Purchase #6 $165.41   5.837%   $175.065   $175.07   $175.05   $175.10  
  Purchase #7 $41.92   3.409%   $43.3491   $43.35   $43.35   $43.30  
  7 purchase totals = $1,099.85       $1,194.5864   $1,194.59   $1,194.60   $1,194.60