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 $59.89   6.708%   $63.9074   $63.91   $63.90   $63.90  
  Purchase #2 $181.55   8.642%   $197.2396   $197.24   $197.25   $197.20  
  Purchase #3 $155.29   9.842%   $170.5736   $170.57   $170.55   $170.60  
  Purchase #4 $164.93   13.103%   $186.5408   $186.54   $186.55   $186.50  
  Purchase #5 $42.95   8.404%   $46.5595   $46.56   $46.55   $46.60  
  Purchase #6 $240.34   4.682%   $251.5927   $251.59   $251.60   $251.60  
  Purchase #7 $90.70   7.719%   $97.7011   $97.70   $97.70   $97.70  
  7 purchase totals = $935.65       $1,014.1147   $1,014.11   $1,014.10   $1,014.10