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 $93.79   3.205%   $96.796   $96.80   $96.80   $96.80  
  Purchase #2 $53.36   3.260%   $55.0995   $55.10   $55.10   $55.10  
  Purchase #3 $96.56   12.787%   $108.9071   $108.91   $108.90   $108.90  
  Purchase #4 $23.48   3.214%   $24.2346   $24.23   $24.25   $24.20  
  Purchase #5 $135.74   8.597%   $147.4096   $147.41   $147.40   $147.40  
  Purchase #6 $19.37   9.425%   $21.1956   $21.20   $21.20   $21.20  
  Purchase #7 $122.91   9.437%   $134.509   $134.51   $134.50   $134.50  
  7 purchase totals = $545.21       $588.1514   $588.16   $588.15   $588.10