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 $191.97   6.417%   $204.2887   $204.29   $204.30   $204.30  
  Purchase #2 $16.45   11.773%   $18.3867   $18.39   $18.40   $18.40  
  Purchase #3 $67.55   12.701%   $76.1295   $76.13   $76.15   $76.10  
  Purchase #4 $171.98   5.551%   $181.5266   $181.53   $181.55   $181.50  
  Purchase #5 $159.58   12.764%   $179.9488   $179.95   $179.95   $179.90  
  Purchase #6 $57.88   4.126%   $60.2681   $60.27   $60.25   $60.30  
  Purchase #7 $214.89   9.347%   $234.9758   $234.98   $235.00   $235.00  
  7 purchase totals = $880.30       $955.5242   $955.54   $955.60   $955.50