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 $241.67   10.750%   $267.6495   $267.65   $267.65   $267.60  
  Purchase #2 $119.80   5.534%   $126.4297   $126.43   $126.45   $126.40  
  Purchase #3 $94.32   4.496%   $98.5606   $98.56   $98.55   $98.60  
  Purchase #4 $58.41   9.717%   $64.0857   $64.09   $64.10   $64.10  
  Purchase #5 $166.68   3.306%   $172.1904   $172.19   $172.20   $172.20  
  Purchase #6 $87.88   12.358%   $98.7402   $98.74   $98.75   $98.70  
  Purchase #7 $192.73   8.147%   $208.4317   $208.43   $208.45   $208.40  
  7 purchase totals = $961.49       $1,036.0878   $1,036.09   $1,036.15   $1,036.00