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 $237.94   8.832%   $258.9549   $258.95   $258.95   $259.00  
  Purchase #2 $139.42   4.219%   $145.3021   $145.30   $145.30   $145.30  
  Purchase #3 $74.33   11.273%   $82.7092   $82.71   $82.70   $82.70  
  Purchase #4 $50.80   3.771%   $52.7157   $52.72   $52.70   $52.70  
  Purchase #5 $86.64   5.154%   $91.1054   $91.11   $91.10   $91.10  
  Purchase #6 $96.59   8.424%   $104.7267   $104.73   $104.75   $104.70  
  Purchase #7 $102.97   4.307%   $107.4049   $107.40   $107.40   $107.40  
  7 purchase totals = $788.69       $842.9189   $842.92   $842.90   $842.90