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 $248.85   7.827%   $268.3275   $268.33   $268.35   $268.30  
  Purchase #2 $79.77   13.518%   $90.5533   $90.55   $90.55   $90.60  
  Purchase #3 $220.79   8.301%   $239.1178   $239.12   $239.10   $239.10  
  Purchase #4 $161.67   3.770%   $167.765   $167.77   $167.75   $167.80  
  Purchase #5 $55.70   7.123%   $59.6675   $59.67   $59.65   $59.70  
  Purchase #6 $248.76   9.790%   $273.1136   $273.11   $273.10   $273.10  
  Purchase #7 $239.38   11.655%   $267.2797   $267.28   $267.30   $267.30  
  7 purchase totals = $1,254.92       $1,365.8244   $1,365.83   $1,365.80   $1,365.90