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 $48.31   11.293%   $53.7656   $53.77   $53.75   $53.80  
  Purchase #2 $181.73   11.364%   $202.3818   $202.38   $202.40   $202.40  
  Purchase #3 $123.76   13.165%   $140.053   $140.05   $140.05   $140.10  
  Purchase #4 $38.25   7.405%   $41.0824   $41.08   $41.10   $41.10  
  Purchase #5 $134.31   7.282%   $144.0905   $144.09   $144.10   $144.10  
  Purchase #6 $118.60   7.821%   $127.8757   $127.88   $127.90   $127.90  
  Purchase #7 $23.36   13.715%   $26.5638   $26.56   $26.55   $26.60  
  7 purchase totals = $668.32       $735.8128   $735.81   $735.85   $736.00