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 $238.88   10.464%   $263.8764   $263.88   $263.90   $263.90  
  Purchase #2 $124.79   12.650%   $140.5759   $140.58   $140.60   $140.60  
  Purchase #3 $246.49   10.605%   $272.6303   $272.63   $272.65   $272.60  
  Purchase #4 $86.73   3.364%   $89.6476   $89.65   $89.65   $89.60  
  Purchase #5 $46.58   5.424%   $49.1065   $49.11   $49.10   $49.10  
  Purchase #6 $174.40   12.283%   $195.8216   $195.82   $195.80   $195.80  
  Purchase #7 $174.67   11.439%   $194.6505   $194.65   $194.65   $194.70  
  7 purchase totals = $1,092.54       $1,206.3088   $1,206.32   $1,206.35   $1,206.30