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 $58.72   11.797%   $65.6472   $65.65   $65.65   $65.60  
  Purchase #2 $218.25   13.657%   $248.0564   $248.06   $248.05   $248.10  
  Purchase #3 $106.73   13.865%   $121.5281   $121.53   $121.55   $121.50  
  Purchase #4 $238.77   6.650%   $254.6482   $254.65   $254.65   $254.60  
  Purchase #5 $156.73   9.610%   $171.7918   $171.79   $171.80   $171.80  
  Purchase #6 $109.97   10.493%   $121.5092   $121.51   $121.50   $121.50  
  Purchase #7 $84.77   6.843%   $90.5708   $90.57   $90.55   $90.60  
  7 purchase totals = $973.94       $1,073.7517   $1,073.76   $1,073.75   $1,073.70