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 $105.41   13.482%   $119.6214   $119.62   $119.60   $119.60  
  Purchase #2 $13.74   3.819%   $14.2647   $14.26   $14.25   $14.30  
  Purchase #3 $62.29   11.493%   $69.449   $69.45   $69.45   $69.40  
  Purchase #4 $12.87   9.370%   $14.0759   $14.08   $14.10   $14.10  
  Purchase #5 $196.60   11.498%   $219.2051   $219.21   $219.20   $219.20  
  Purchase #6 $220.35   9.782%   $241.9046   $241.90   $241.90   $241.90  
  Purchase #7 $14.60   4.200%   $15.2132   $15.21   $15.20   $15.20  
  7 purchase totals = $625.86       $693.7339   $693.73   $693.70   $693.70