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 $164.89   10.346%   $181.9495   $181.95   $181.95   $181.90  
  Purchase #2 $211.45   11.291%   $235.3248   $235.32   $235.30   $235.30  
  Purchase #3 $239.58   4.726%   $250.9026   $250.90   $250.90   $250.90  
  Purchase #4 $31.43   8.329%   $34.0478   $34.05   $34.05   $34.00  
  Purchase #5 $8.79   9.182%   $9.5971   $9.60   $9.60   $9.60  
  Purchase #6 $217.25   13.468%   $246.5092   $246.51   $246.50   $246.50  
  Purchase #7 $109.61   13.813%   $124.7504   $124.75   $124.75   $124.80  
  7 purchase totals = $983.00       $1,083.0814   $1,083.08   $1,083.05   $1,083.00