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 $236.32   9.833%   $259.5573   $259.56   $259.55   $259.60  
  Purchase #2 $214.58   9.860%   $235.7376   $235.74   $235.75   $235.70  
  Purchase #3 $122.31   4.106%   $127.332   $127.33   $127.35   $127.30  
  Purchase #4 $171.48   8.658%   $186.3267   $186.33   $186.35   $186.30  
  Purchase #5 $179.52   13.439%   $203.6457   $203.65   $203.65   $203.60  
  Purchase #6 $53.99   5.438%   $56.926   $56.93   $56.95   $56.90  
  Purchase #7 $60.43   9.266%   $66.0294   $66.03   $66.05   $66.00  
  7 purchase totals = $1,038.63       $1,135.5547   $1,135.57   $1,135.65   $1,135.40