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 $226.35   11.868%   $253.2132   $253.21   $253.20   $253.20  
  Purchase #2 $177.38   8.817%   $193.0196   $193.02   $193.00   $193.00  
  Purchase #3 $68.58   8.313%   $74.2811   $74.28   $74.30   $74.30  
  Purchase #4 $230.94   7.430%   $248.0988   $248.10   $248.10   $248.10  
  Purchase #5 $233.29   6.639%   $248.7781   $248.78   $248.80   $248.80  
  Purchase #6 $124.85   7.278%   $133.9366   $133.94   $133.95   $133.90  
  Purchase #7 $179.83   11.707%   $200.8827   $200.88   $200.90   $200.90  
  7 purchase totals = $1,241.22       $1,352.2101   $1,352.21   $1,352.25   $1,352.20