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 $53.36   5.604%   $56.3503   $56.35   $56.35   $56.40  
  Purchase #2 $221.55   6.142%   $235.1576   $235.16   $235.15   $235.20  
  Purchase #3 $137.71   5.778%   $145.6669   $145.67   $145.65   $145.70  
  Purchase #4 $28.70   10.133%   $31.6082   $31.61   $31.60   $31.60  
  Purchase #5 $122.94   3.798%   $127.6093   $127.61   $127.60   $127.60  
  Purchase #6 $201.65   4.808%   $211.3453   $211.35   $211.35   $211.30  
  Purchase #7 $224.41   9.655%   $246.0768   $246.08   $246.10   $246.10  
  7 purchase totals = $990.32       $1,053.8144   $1,053.83   $1,053.80   $1,053.90