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 $216.87   12.359%   $243.673   $243.67   $243.65   $243.70  
  Purchase #2 $171.53   12.264%   $192.5664   $192.57   $192.55   $192.60  
  Purchase #3 $162.67   8.539%   $176.5604   $176.56   $176.55   $176.60  
  Purchase #4 $197.99   11.367%   $220.4955   $220.50   $220.50   $220.50  
  Purchase #5 $57.81   13.759%   $65.7641   $65.76   $65.75   $65.80  
  Purchase #6 $41.39   6.860%   $44.2294   $44.23   $44.25   $44.20  
  Purchase #7 $198.82   13.192%   $225.0483   $225.05   $225.05   $225.00  
  7 purchase totals = $1,047.08       $1,168.3371   $1,168.34   $1,168.30   $1,168.40