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 $144.54   8.316%   $156.5599   $156.56   $156.55   $156.60  
  Purchase #2 $238.77   12.281%   $268.0933   $268.09   $268.10   $268.10  
  Purchase #3 $14.27   12.732%   $16.0869   $16.09   $16.10   $16.10  
  Purchase #4 $108.64   3.648%   $112.6032   $112.60   $112.60   $112.60  
  Purchase #5 $127.84   4.843%   $134.0313   $134.03   $134.05   $134.00  
  Purchase #6 $124.68   5.551%   $131.601   $131.60   $131.60   $131.60  
  Purchase #7 $217.48   7.119%   $232.9624   $232.96   $232.95   $233.00  
  7 purchase totals = $976.22       $1,051.9380   $1,051.93   $1,051.95   $1,052.00