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 $208.39   12.541%   $234.5242   $234.52   $234.50   $234.50  
  Purchase #2 $114.29   13.378%   $129.5797   $129.58   $129.60   $129.60  
  Purchase #3 $166.82   5.524%   $176.0351   $176.04   $176.05   $176.00  
  Purchase #4 $217.72   10.791%   $241.2142   $241.21   $241.20   $241.20  
  Purchase #5 $49.39   11.570%   $55.1044   $55.10   $55.10   $55.10  
  Purchase #6 $109.97   12.746%   $123.9868   $123.99   $124.00   $124.00  
  Purchase #7 $86.80   13.333%   $98.373   $98.37   $98.35   $98.40  
  7 purchase totals = $953.38       $1,058.8174   $1,058.81   $1,058.80   $1,058.80