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 $122.86   10.122%   $135.2959   $135.30   $135.30   $135.30  
  Purchase #2 $201.26   8.509%   $218.3852   $218.39   $218.40   $218.40  
  Purchase #3 $152.56   10.503%   $168.5834   $168.58   $168.60   $168.60  
  Purchase #4 $187.79   8.382%   $203.5306   $203.53   $203.55   $203.50  
  Purchase #5 $153.59   4.597%   $160.6505   $160.65   $160.65   $160.70  
  Purchase #6 $140.62   13.111%   $159.0567   $159.06   $159.05   $159.10  
  Purchase #7 $56.60   4.599%   $59.203   $59.20   $59.20   $59.20  
  7 purchase totals = $1,015.28       $1,104.7053   $1,104.71   $1,104.75   $1,104.80