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 $96.99   10.217%   $106.8995   $106.90   $106.90   $106.90  
  Purchase #2 $46.99   13.539%   $53.352   $53.35   $53.35   $53.40  
  Purchase #3 $225.97   10.445%   $249.5726   $249.57   $249.55   $249.60  
  Purchase #4 $118.41   4.597%   $123.8533   $123.85   $123.85   $123.90  
  Purchase #5 $202.79   7.467%   $217.9323   $217.93   $217.95   $217.90  
  Purchase #6 $49.93   6.721%   $53.2858   $53.29   $53.30   $53.30  
  Purchase #7 $243.47   8.224%   $263.493   $263.49   $263.50   $263.50  
  7 purchase totals = $984.55       $1,068.3885   $1,068.38   $1,068.40   $1,068.50