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 $182.67   10.209%   $201.3188   $201.32   $201.30   $201.30  
  Purchase #2 $180.52   12.771%   $203.5742   $203.57   $203.55   $203.60  
  Purchase #3 $29.76   7.538%   $32.0033   $32.00   $32.00   $32.00  
  Purchase #4 $53.90   12.482%   $60.6278   $60.63   $60.65   $60.60  
  Purchase #5 $130.46   12.358%   $146.5822   $146.58   $146.60   $146.60  
  Purchase #6 $162.62   5.728%   $171.9349   $171.93   $171.95   $171.90  
  Purchase #7 $176.84   5.338%   $186.2797   $186.28   $186.30   $186.30  
  7 purchase totals = $916.77       $1,002.3209   $1,002.31   $1,002.35   $1,002.30