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 $208.96   12.705%   $235.5084   $235.51   $235.50   $235.50  
  Purchase #2 $99.43   10.331%   $109.7021   $109.70   $109.70   $109.70  
  Purchase #3 $230.49   11.656%   $257.3559   $257.36   $257.35   $257.40  
  Purchase #4 $124.65   11.593%   $139.1007   $139.10   $139.10   $139.10  
  Purchase #5 $63.26   13.253%   $71.6438   $71.64   $71.65   $71.60  
  Purchase #6 $69.92   6.821%   $74.6892   $74.69   $74.70   $74.70  
  Purchase #7 $190.96   6.379%   $203.1413   $203.14   $203.15   $203.10  
  7 purchase totals = $987.67       $1,091.1414   $1,091.14   $1,091.15   $1,091.10