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 $213.85   12.193%   $239.9247   $239.92   $239.90   $239.90  
  Purchase #2 $63.64   8.760%   $69.2149   $69.21   $69.20   $69.20  
  Purchase #3 $187.85   3.350%   $194.143   $194.14   $194.15   $194.10  
  Purchase #4 $135.28   8.349%   $146.5745   $146.57   $146.55   $146.60  
  Purchase #5 $181.48   6.170%   $192.6773   $192.68   $192.70   $192.70  
  Purchase #6 $10.52   11.250%   $11.7035   $11.70   $11.70   $11.70  
  Purchase #7 $189.43   10.113%   $208.5871   $208.59   $208.60   $208.60  
  7 purchase totals = $982.05       $1,062.8250   $1,062.81   $1,062.80   $1,062.80