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 $237.35   5.195%   $249.6803   $249.68   $249.70   $249.70  
  Purchase #2 $194.26   4.160%   $202.3412   $202.34   $202.35   $202.30  
  Purchase #3 $53.57   10.285%   $59.0797   $59.08   $59.10   $59.10  
  Purchase #4 $95.55   12.474%   $107.4689   $107.47   $107.45   $107.50  
  Purchase #5 $76.37   13.644%   $86.7899   $86.79   $86.80   $86.80  
  Purchase #6 $126.59   3.295%   $130.7611   $130.76   $130.75   $130.80  
  Purchase #7 $120.35   9.119%   $131.3247   $131.32   $131.30   $131.30  
  7 purchase totals = $904.04       $967.4458   $967.44   $967.45   $967.50