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 $30.89   5.352%   $32.5432   $32.54   $32.55   $32.50  
  Purchase #2 $71.28   12.698%   $80.3311   $80.33   $80.35   $80.30  
  Purchase #3 $212.55   13.382%   $240.9934   $240.99   $241.00   $241.00  
  Purchase #4 $161.78   6.147%   $171.7246   $171.72   $171.70   $171.70  
  Purchase #5 $236.33   10.169%   $260.3624   $260.36   $260.35   $260.40  
  Purchase #6 $49.90   4.227%   $52.0093   $52.01   $52.00   $52.00  
  Purchase #7 $84.30   12.253%   $94.6293   $94.63   $94.65   $94.60  
  7 purchase totals = $847.03       $932.5933   $932.58   $932.60   $932.50