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 $56.91   12.195%   $63.8502   $63.85   $63.85   $63.90  
  Purchase #2 $238.59   11.372%   $265.7225   $265.72   $265.70   $265.70  
  Purchase #3 $212.82   10.417%   $234.9895   $234.99   $235.00   $235.00  
  Purchase #4 $155.90   13.155%   $176.4086   $176.41   $176.40   $176.40  
  Purchase #5 $61.48   4.849%   $64.4612   $64.46   $64.45   $64.50  
  Purchase #6 $199.76   9.394%   $218.5255   $218.53   $218.55   $218.50  
  Purchase #7 $190.73   10.747%   $211.2278   $211.23   $211.25   $211.20  
  7 purchase totals = $1,116.19       $1,235.1853   $1,235.19   $1,235.20   $1,235.20