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 $25.68   5.857%   $27.1841   $27.18   $27.20   $27.20  
  Purchase #2 $189.77   7.436%   $203.8813   $203.88   $203.90   $203.90  
  Purchase #3 $108.32   11.349%   $120.6132   $120.61   $120.60   $120.60  
  Purchase #4 $235.25   6.665%   $250.9294   $250.93   $250.95   $250.90  
  Purchase #5 $242.54   4.445%   $253.3209   $253.32   $253.30   $253.30  
  Purchase #6 $119.51   5.709%   $126.3328   $126.33   $126.35   $126.30  
  Purchase #7 $145.25   4.179%   $151.32   $151.32   $151.30   $151.30  
  7 purchase totals = $1,066.32       $1,133.5817   $1,133.57   $1,133.60   $1,133.50