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 $24.82   9.483%   $27.1737   $27.17   $27.15   $27.20  
  Purchase #2 $117.49   7.560%   $126.3722   $126.37   $126.35   $126.40  
  Purchase #3 $225.75   7.592%   $242.8889   $242.89   $242.90   $242.90  
  Purchase #4 $230.55   9.329%   $252.058   $252.06   $252.05   $252.10  
  Purchase #5 $89.60   13.748%   $101.9182   $101.92   $101.90   $101.90  
  Purchase #6 $168.31   13.327%   $190.7407   $190.74   $190.75   $190.70  
  Purchase #7 $177.73   13.867%   $202.3758   $202.38   $202.40   $202.40  
  7 purchase totals = $1,034.25       $1,143.5275   $1,143.53   $1,143.50   $1,143.60