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 $237.83   9.553%   $260.5499   $260.55   $260.55   $260.50  
  Purchase #2 $211.45   7.163%   $226.5962   $226.60   $226.60   $226.60  
  Purchase #3 $215.85   12.787%   $243.4507   $243.45   $243.45   $243.50  
  Purchase #4 $55.98   11.343%   $62.3298   $62.33   $62.35   $62.30  
  Purchase #5 $16.57   4.188%   $17.264   $17.26   $17.25   $17.30  
  Purchase #6 $81.72   3.535%   $84.6088   $84.61   $84.60   $84.60  
  Purchase #7 $207.43   13.393%   $235.2111   $235.21   $235.20   $235.20  
  7 purchase totals = $1,026.83       $1,130.0105   $1,130.01   $1,130.00   $1,130.00