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 $188.36   9.666%   $206.5669   $206.57   $206.55   $206.60  
  Purchase #2 $174.76   3.349%   $180.6127   $180.61   $180.60   $180.60  
  Purchase #3 $24.63   8.762%   $26.7881   $26.79   $26.80   $26.80  
  Purchase #4 $196.54   6.741%   $209.7888   $209.79   $209.80   $209.80  
  Purchase #5 $235.58   4.764%   $246.803   $246.80   $246.80   $246.80  
  Purchase #6 $212.77   6.866%   $227.3788   $227.38   $227.40   $227.40  
  Purchase #7 $123.89   10.611%   $137.036   $137.04   $137.05   $137.00  
  7 purchase totals = $1,156.53       $1,234.9743   $1,234.98   $1,235.00   $1,235.00