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 $51.46   9.865%   $56.5365   $56.54   $56.55   $56.50  
  Purchase #2 $126.86   5.182%   $133.4339   $133.43   $133.45   $133.40  
  Purchase #3 $122.56   11.434%   $136.5735   $136.57   $136.55   $136.60  
  Purchase #4 $230.89   12.782%   $260.4024   $260.40   $260.40   $260.40  
  Purchase #5 $156.54   9.656%   $171.6555   $171.66   $171.65   $171.70  
  Purchase #6 $195.35   11.223%   $217.2741   $217.27   $217.25   $217.30  
  Purchase #7 $35.94   4.832%   $37.6766   $37.68   $37.70   $37.70  
  7 purchase totals = $919.60       $1,013.5525   $1,013.55   $1,013.55   $1,013.60