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 $145.76   3.671%   $151.1108   $151.11   $151.10   $151.10  
  Purchase #2 $23.35   5.735%   $24.6891   $24.69   $24.70   $24.70  
  Purchase #3 $219.55   9.848%   $241.1713   $241.17   $241.15   $241.20  
  Purchase #4 $164.51   7.739%   $177.2414   $177.24   $177.25   $177.20  
  Purchase #5 $119.53   7.568%   $128.576   $128.58   $128.60   $128.60  
  Purchase #6 $47.94   13.693%   $54.5044   $54.50   $54.50   $54.50  
  Purchase #7 $75.39   11.857%   $84.329   $84.33   $84.35   $84.30  
  7 purchase totals = $796.03       $861.6220   $861.62   $861.65   $861.60