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 $240.60   11.280%   $267.7397   $267.74   $267.75   $267.70  
  Purchase #2 $248.51   13.344%   $281.6712   $281.67   $281.65   $281.70  
  Purchase #3 $189.35   11.326%   $210.7958   $210.80   $210.80   $210.80  
  Purchase #4 $77.76   9.302%   $84.9932   $84.99   $85.00   $85.00  
  Purchase #5 $89.63   9.394%   $98.0498   $98.05   $98.05   $98.00  
  Purchase #6 $63.71   4.506%   $66.5808   $66.58   $66.60   $66.60  
  Purchase #7 $23.41   3.461%   $24.2202   $24.22   $24.20   $24.20  
  7 purchase totals = $932.97       $1,034.0507   $1,034.05   $1,034.05   $1,034.00