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 $239.86   12.245%   $269.2309   $269.23   $269.25   $269.20  
  Purchase #2 $145.88   11.133%   $162.1208   $162.12   $162.10   $162.10  
  Purchase #3 $153.66   13.524%   $174.441   $174.44   $174.45   $174.40  
  Purchase #4 $143.58   8.344%   $155.5603   $155.56   $155.55   $155.60  
  Purchase #5 $238.40   12.428%   $268.0284   $268.03   $268.05   $268.00  
  Purchase #6 $67.67   6.169%   $71.8446   $71.84   $71.85   $71.80  
  Purchase #7 $210.56   5.404%   $221.9387   $221.94   $221.95   $221.90  
  7 purchase totals = $1,199.61       $1,323.1647   $1,323.16   $1,323.20   $1,323.00